# UnitFYI

> Comprehensive unit conversion reference for developers, scientists, and engineers. 200 units across 20 measurement categories with Decimal-precision conversion, 157 glossary terms, 5 interactive tools, and N-squared comparison pages. All conversions computed on-the-fly with sub-millisecond pure-Python engine.

## Data Scope
- 200 units across 20 measurement categories (length, weight, temperature, volume, area, speed, time, data-storage, pressure, energy, frequency, force, power, angle, fuel-economy, data-transfer, density, torque, cooking, typography)
- Decimal-precision conversion engine — no floating-point rounding errors
- N-squared unit pair conversion pages (e.g. /length/meter-to-foot/)
- N-squared unit comparison pages (e.g. /length/compare/meter-vs-foot/)
- Specific value conversion (e.g. /length/meter-to-foot/100/)
- 157 glossary terms covering measurement science and metrology
- 5 interactive tools: converter, quick-convert, table-generator, comparison, recipe-converter
- 15 languages: en, ko, ja, zh-hans, es, fr, de, pt, ru, vi, tr, ar, hi, th, id

## URL Patterns
- Append `.md` to any URL for plain-text markdown format.
- i18n: URL prefix `/{lang}` for non-English (ko, ja, zh-hans, es, fr, de, pt, ru, vi, tr, ar, hi, th, id).
- `/` — Homepage — browse all 20 measurement categories (e.g. `/`)
- `/{category}/` — Category detail with all units (e.g. `/length/`)
- `/{category}/unit/{unit}/` — Unit detail page (e.g. `/length/unit/meter/`)
- `/{category}/{from}-to-{to}/` — Unit pair conversion page (N² pSEO) (e.g. `/length/meter-to-foot/`)
- `/{category}/{from}-to-{to}/{value}/` — Specific value conversion (e.g. `/length/meter-to-foot/100/`)
- `/{category}/compare/{a}-vs-{b}/` — Unit comparison page (N² pSEO) (e.g. `/length/compare/meter-vs-foot/`)
- `/glossary/` — Measurement glossary index (e.g. `/glossary/`)
- `/glossary/{slug}/` — Glossary term detail (e.g. `/glossary/metric-system/`)
- `/blog/` — Measurement science articles (e.g. `/blog/`)
- `/blog/{slug}/` — Blog article detail (e.g. `/blog/si-units-history/`)
- `/tools/` — Interactive tools index (e.g. `/tools/`)
- `/tools/{slug}/` — Tool page (e.g. `/tools/converter/`)
- `/search/` — Search units, categories, glossary (e.g. `/search/?q=meter`)

## Measurement Categories (20)
- [Length (meter, foot, mile, ...)](https://unitfyi.com/length/)
- [Weight (kilogram, pound, ounce, ...)](https://unitfyi.com/weight/)
- [Temperature (celsius, fahrenheit, kelvin)](https://unitfyi.com/temperature/)
- [Volume (liter, gallon, cup, ...)](https://unitfyi.com/volume/)
- [Area (sq meter, acre, hectare, ...)](https://unitfyi.com/area/)
- [Speed (m/s, km/h, mph, ...)](https://unitfyi.com/speed/)
- [Time (second, minute, hour, ...)](https://unitfyi.com/time/)
- [Data Storage (byte, KB, MB, GB, TB, ...)](https://unitfyi.com/data-storage/)
- [Pressure (pascal, bar, psi, atm, ...)](https://unitfyi.com/pressure/)
- [Energy (joule, calorie, BTU, kWh, ...)](https://unitfyi.com/energy/)
- [Frequency (hertz, kHz, MHz, GHz, ...)](https://unitfyi.com/frequency/)
- [Force (newton, dyne, pound-force, ...)](https://unitfyi.com/force/)
- [Power (watt, horsepower, BTU/h, ...)](https://unitfyi.com/power/)
- [Angle (radian, degree, gradian, ...)](https://unitfyi.com/angle/)
- [Fuel Economy (km/L, MPG, L/100km, ...)](https://unitfyi.com/fuel-economy/)
- [Data Transfer (bps, Kbps, Mbps, Gbps, ...)](https://unitfyi.com/data-transfer/)
- [Density (kg/m³, g/cm³, lb/ft³, ...)](https://unitfyi.com/density/)
- [Torque (N·m, ft·lb, kgf·m, ...)](https://unitfyi.com/torque/)
- [Cooking (mL, tsp, tbsp, cup, ...)](https://unitfyi.com/cooking/)
- [Typography (pixel, point, em, rem, ...)](https://unitfyi.com/typography/)

## Interactive Tools
- [Unit Converter](https://unitfyi.com/tools/converter/)
- [Quick Convert](https://unitfyi.com/tools/quick-convert/)
- [Conversion Table Generator](https://unitfyi.com/tools/table-generator/)
- [Unit Comparison](https://unitfyi.com/tools/comparison/)
- [Recipe Converter](https://unitfyi.com/tools/recipe-converter/)

## Reference
- [Measurement Glossary (157 terms)](https://unitfyi.com/glossary/)
- [Blog — Measurement Science Articles](https://unitfyi.com/blog/)

## Embed Widget
- [UnitFYI Widget Docs](https://widget.unitfyi.com)
- [unitfyi-embed on npm](https://www.npmjs.com/package/unitfyi-embed)
- [unitfyi-embed on GitHub](https://github.com/fyipedia/unitfyi-embed)

## REST API

Free REST API. No authentication required. JSON responses. CORS enabled.

| Method | Endpoint | Description |
|--------|----------|-------------|
| GET | `/api/convert/?from={unit}&to={unit}&value={n}` | Convert a value between units |
| GET | `/api/categories/` | List all 20 measurement categories |
| GET | `/api/categories/{slug}/` | Category detail with all units |
| GET | `/api/units/` | List all 200 units |
| GET | `/api/unit/{slug}/` | Unit detail with conversion factors |
| GET | `/api/convert/table/` | Conversion table for a category |
| GET | `/api/glossary/` | List all glossary terms |
| GET | `/api/glossary/{slug}/` | Glossary term detail |
| GET | `/api/blog/posts/` | Blog posts list |
| GET | `/api/blog/posts/{slug}/` | Blog post detail |
| GET | `/api/tools/` | List interactive tools |
| GET | `/api/search/` | Search units, categories, glossary |
| GET | `/api/v1/glossary/` | Glossary terms (DRF ViewSet, paginated) |
| GET | `/api/v1/tools/` | Tools (DRF ViewSet) |
| GET | `/api/v1/faqs/` | FAQs (DRF ViewSet) |
| GET | `/api/v1/search/?q={query}` | Unified search (DRF) |
| GET | `/api/v1/stats/` | Site statistics |

```bash
curl -s "https://unitfyi.com/api/convert/?from=meter&to=foot&value=100"
```

[API Docs](https://unitfyi.com/developers/) · [OpenAPI Spec](https://unitfyi.com/api/openapi.json)

## Developer Tools
- **PyPI**: `pip install unitfyi` — [unitfyi](https://pypi.org/project/unitfyi/) — Unit conversion with Decimal precision, 220 units (v0.1.2)
- **npm**: `npm install unitfyi` — [unitfyi](https://www.npmjs.com/package/unitfyi) — TypeScript unit conversion utilities (v0.1.1)
- **Embed Widget**: [unitfyi-embed](https://widget.unitfyi.com)

## Utility FYI Family

Part of [FYIPedia](https://fyipedia.com) developer tools ecosystem.
- [TimeFYI](https://timefyi.com) — Timezone ops, business hours, sunrise/sunset
- [HolidayFYI](https://holidayfyi.com) — Holiday dates, Easter calculation, 200+ countries
- [NameFYI](https://namefyi.com) — Korean romanization, Five Elements, CJK strokes

## Images (CDN)

OG images at https://cdn.unitfyi.com/og/
- https://cdn.unitfyi.com/og/homepage.png

## Measurement Glossary
- [Absolute Zero — The lowest possible temperature: 0 K, -273.15°C, or -459.67°F.](https://unitfyi.com/glossary/absolute-zero/)
- [Accuracy — How close a measurement is to the true value of the quantity being measured.](https://unitfyi.com/glossary/accuracy/)
- [Acre — An imperial unit of area equal to 43,560 square feet or about 4,047 square meter](https://unitfyi.com/glossary/acre-def/)
- [Ampere — The SI base unit of electric current.](https://unitfyi.com/glossary/ampere/)
- [Astronomical Unit — The average distance from Earth to the Sun: 149,597,870,700 meters.](https://unitfyi.com/glossary/astronomical-unit-def/)
- [Avogadro's Number — The exact number of elementary entities (atoms, molecules, or ions) in one mole ](https://unitfyi.com/glossary/avogadro-number-def/)
- [Avoirdupois — The standard system of weights based on the 16-ounce pound, used for everyday go](https://unitfyi.com/glossary/avoirdupois/)
- [Baker's Percentage — Baker's percentage is a notation system where every ingredient in a bread recipe](https://unitfyi.com/glossary/bakers-percentage-def/)
- [Bandwidth — Bandwidth is the maximum data transfer capacity of a communication channel, typi](https://unitfyi.com/glossary/bandwidth-def/)
- [Bar — A unit of pressure equal to 100,000 pascals, slightly less than standard atmosph](https://unitfyi.com/glossary/bar-def/)
- [Barrel (Oil) — A unit of volume for crude oil, equal to 42 US gallons (158.987 liters).](https://unitfyi.com/glossary/barrel-def/)
- [Base Unit — A fundamental unit from which other units in a system are derived.](https://unitfyi.com/glossary/base-unit/)
- [Bearing — A bearing is the horizontal direction of travel or of a target, measured clockwi](https://unitfyi.com/glossary/bearing-def/)
- [Becquerel — The SI unit of radioactivity, equal to one nuclear disintegration (decay event) ](https://unitfyi.com/glossary/becquerel-def/)
- [Binary Prefix — Binary prefixes (KiB, MiB, GiB) denote powers of 1024, in contrast to metric SI ](https://unitfyi.com/glossary/binary-prefix-def/)
- [Bit and Byte — A bit is the smallest unit of digital information, representing a 0 or 1; a byte](https://unitfyi.com/glossary/bit-and-byte/)
- [Blood Pressure Units — Blood pressure is measured in millimeters of mercury (mmHg), expressed as two va](https://unitfyi.com/glossary/blood-pressure-units/)
- [BMI (Body Mass Index) — The Body Mass Index (BMI) is a screening metric calculated by dividing a person'](https://unitfyi.com/glossary/body-mass-index/)
- [Boltzmann Constant — A fundamental physical constant with the exact value 1.380649 × 10⁻²³ J/K, relat](https://unitfyi.com/glossary/boltzmann-constant-def/)
- [BTU (British Thermal Unit) — The amount of heat needed to raise the temperature of one pound of water by one ](https://unitfyi.com/glossary/btu-def/)
- [Bushel — A dry volume unit used for agricultural commodities: the US bushel equals 35.239](https://unitfyi.com/glossary/bushel-def/)
- [Calibration — The process of comparing and adjusting a measuring instrument against a known re](https://unitfyi.com/glossary/calibration-def/)
- [Calorie — A unit of energy. The small calorie (cal) heats 1g of water by 1°C; the food Cal](https://unitfyi.com/glossary/calorie-def/)
- [Candela — The SI base unit of luminous intensity, defined by fixing the luminous efficacy ](https://unitfyi.com/glossary/candela-def/)
- [Cap Height — Cap height is the typographic measurement of the height of a flat uppercase lett](https://unitfyi.com/glossary/cap-height-def/)
- [Carat — A unit of mass for gemstones, equal to 200 milligrams (0.2 grams).](https://unitfyi.com/glossary/carat-def/)
- [Celsius — A metric temperature scale where 0°C is the freezing point of water and 100°C is](https://unitfyi.com/glossary/celsius-def/)
- [CGS System — A metric unit system based on the centimeter, gram, and second as fundamental un](https://unitfyi.com/glossary/cgs-system/)
- [Chi (尺) — The chi (尺) is a traditional Chinese unit of length now standardized in the Peop](https://unitfyi.com/glossary/chi-def/)
- [Clock Speed — Clock speed is the frequency at which a processor executes cycles, measured in h](https://unitfyi.com/glossary/clock-speed-def/)
- [Conversion Factor — A numerical multiplier used to convert a quantity from one unit to another.](https://unitfyi.com/glossary/conversion-factor/)
- [Coulomb — The SI unit of electric charge, defined as the charge transported by a current o](https://unitfyi.com/glossary/coulomb-def/)
- [Cubit — The cubit is an ancient unit of length based on the distance from the elbow to t](https://unitfyi.com/glossary/cubit-def/)
- [Cup (Measurement) — A cooking volume unit. The US cup equals 236.588 ml; the metric cup is 250 ml.](https://unitfyi.com/glossary/cup-measurement/)
- [Dash & Pinch — A dash is an informal culinary measure of approximately 1/8 teaspoon (0.6 mL), a](https://unitfyi.com/glossary/dash-pinch-def/)
- [Dead Reckoning — Dead reckoning is the process of estimating a vessel's or vehicle's current posi](https://unitfyi.com/glossary/dead-reckoning-def/)
- [Decimal System — A base-10 numbering system in which each place value is ten times the next small](https://unitfyi.com/glossary/decimal-system/)
- [Derived Quantity — A physical quantity defined by a mathematical combination of SI base quantities ](https://unitfyi.com/glossary/derived-quantity/)
- [Derived Unit — A unit of measurement expressed as a combination of base units.](https://unitfyi.com/glossary/derived-unit/)
- [Dimensional Analysis — A method of converting units by multiplying by conversion factors that equal 1.](https://unitfyi.com/glossary/dimensional-analysis/)
- [Dimensional Homogeneity — The requirement that all terms in a physically valid equation must have identica](https://unitfyi.com/glossary/dimensional-homogeneity/)
- [DPI & PPI — DPI (dots per inch) measures print output resolution; PPI (pixels per inch) meas](https://unitfyi.com/glossary/dpi-ppi-def/)
- [Electronvolt — A unit of energy equal to the kinetic energy gained by an electron accelerated t](https://unitfyi.com/glossary/electronvolt-def/)
- [Em — The em is a relative typographic unit equal to the current element's font size; ](https://unitfyi.com/glossary/em-def/)
- [Entropy — Entropy is a thermodynamic quantity measuring the degree of disorder or randomne](https://unitfyi.com/glossary/entropy-def/)
- [Error Margin — The range above and below a measured or estimated value within which the true va](https://unitfyi.com/glossary/error-margin-def/)
- [Farad — The SI unit of electrical capacitance, defined as the capacitance of a capacitor](https://unitfyi.com/glossary/farad-def/)
- [Fathom — A unit of length equal to 6 feet (1.8288 m), used to measure water depth.](https://unitfyi.com/glossary/fathom-def/)
- [Fluid Ounce — A fluid ounce is a unit of liquid volume, with the US fluid ounce equal to 29.57](https://unitfyi.com/glossary/fluid-ounce-def/)
- [Foot — An imperial unit of length equal to 12 inches or exactly 0.3048 meters, subdivid](https://unitfyi.com/glossary/foot-def/)
- [Furlong — A unit of length equal to 1/8 of a mile (201.168 m).](https://unitfyi.com/glossary/furlong-def/)
- [Gallon — A volume unit with two definitions: the US gallon equals 3.785411784 liters; the](https://unitfyi.com/glossary/gallon-def/)
- [Grain — A unit of mass equal to 1/7000 of a pound (64.799 mg).](https://unitfyi.com/glossary/grain-def/)
- [Gram — A metric unit of mass equal to one-thousandth of a kilogram (10⁻³ kg), originall](https://unitfyi.com/glossary/gram-def/)
- [Great Circle — A great circle is any circle on a sphere whose center coincides with the sphere'](https://unitfyi.com/glossary/great-circle-def/)
- [Half-Life — Half-life is the time required for exactly half of the radioactive atoms in a sa](https://unitfyi.com/glossary/half-life-def/)
- [Hand — A unit of length equal to exactly 4 inches (10.16 cm), used internationally to m](https://unitfyi.com/glossary/hand-unit-def/)
- [Hectare — A metric unit of area equal to 10,000 square meters or 2.471 acres.](https://unitfyi.com/glossary/hectare-def/)
- [Hertz — The SI unit of frequency, equal to one cycle per second.](https://unitfyi.com/glossary/hertz-def/)
- [Horsepower — A unit of power. Mechanical horsepower equals approximately 745.7 watts.](https://unitfyi.com/glossary/horsepower-def/)
- [Imperial System — A system of measurement used primarily in the United States, based on historical](https://unitfyi.com/glossary/imperial-system/)
- [Inch — An imperial unit of length defined as exactly 2.54 centimeters or 1/12 of a foot](https://unitfyi.com/glossary/inch-def/)
- [International System of Units (SI) — The modern metric system of measurement, accepted worldwide for scientific and c](https://unitfyi.com/glossary/si-system/)
- [Interpolation — The estimation of a value between two known data points by assuming a functional](https://unitfyi.com/glossary/interpolation-def/)
- [Jigger — A jigger is a bartending measure equal to 1.5 US fluid ounces (44.36 mL), used a](https://unitfyi.com/glossary/jigger-def/)
- [Joule — The SI unit of energy, equal to the work done by a force of one newton acting ov](https://unitfyi.com/glossary/joule-def/)
- [Kelvin — The SI base unit of temperature, starting at absolute zero.](https://unitfyi.com/glossary/kelvin/)
- [Kilogram — The SI base unit of mass, defined by the Planck constant.](https://unitfyi.com/glossary/kilogram/)
- [Kilometer — A metric unit of length equal to 1,000 meters or approximately 0.621371 miles.](https://unitfyi.com/glossary/kilometer-def/)
- [Knot — A unit of speed equal to one nautical mile per hour (1.852 km/h).](https://unitfyi.com/glossary/knot-def/)
- [Latency — Latency is the time delay between a data packet being sent from a source and rec](https://unitfyi.com/glossary/latency-def/)
- [Latitude & Longitude — Latitude and longitude are a geographic coordinate system using angular degrees ](https://unitfyi.com/glossary/latitude-longitude-def/)
- [League — The league is a unit of distance historically defined as the distance a person o](https://unitfyi.com/glossary/league-def/)
- [Light-Year — The distance light travels in one year in vacuum: approximately 9.461 trillion k](https://unitfyi.com/glossary/light-year-def/)
- [Liter — A metric unit of volume equal to one cubic decimeter (1 dm³ = 1,000 cm³ = 1,000 ](https://unitfyi.com/glossary/liter-def/)
- [Lumen — The SI derived unit of luminous flux, measuring the total quantity of visible li](https://unitfyi.com/glossary/lumen-def/)
- [Lux — The SI unit of illuminance, measuring luminous flux received per unit area: one ](https://unitfyi.com/glossary/lux-def/)
- [Mach Number — The ratio of an object's speed to the speed of sound in the surrounding medium.](https://unitfyi.com/glossary/mach-number/)
- [Magnetic Declination — Magnetic declination is the angle between true (geographic) north and magnetic n](https://unitfyi.com/glossary/magnetic-declination-def/)
- [Measurement Uncertainty — A parameter, associated with a measurement result, that characterizes the disper](https://unitfyi.com/glossary/uncertainty-def/)
- [Meter — The SI base unit of length, defined as the distance light travels in 1/299,792,4](https://unitfyi.com/glossary/meter/)
- [Metrication — The process of adopting the metric system as a country's standard system of meas](https://unitfyi.com/glossary/metrication/)
- [Metric Cup — The metric cup is a unit of volume equal to exactly 250 mL, used as the standard](https://unitfyi.com/glossary/metric-cup-def/)
- [Metric Prefix — A prefix that indicates a decimal multiple or fraction of a unit (kilo-, mega-, ](https://unitfyi.com/glossary/metric-prefix/)
- [Metric System — A decimal-based international system of measurement built on seven SI base units](https://unitfyi.com/glossary/metric-system-def/)
- [Mile — An imperial unit of length equal to 5,280 feet, 1,760 yards, or exactly 1.609344](https://unitfyi.com/glossary/mile-def/)
- [MKS System — A metric unit system based on the meter, kilogram, and second, which served as t](https://unitfyi.com/glossary/mks-system/)
- [Mole — The SI base unit for amount of substance, defined as exactly 6.02214076×10²³ ele](https://unitfyi.com/glossary/mole-def/)
- [Nautical Mile — A unit of distance used in sea and air navigation, equal to 1,852 meters.](https://unitfyi.com/glossary/nautical-mile-def/)
- [Newton — The SI unit of force, equal to the force needed to accelerate 1 kg at 1 m/s².](https://unitfyi.com/glossary/newton-def/)
- [Ohm — The SI unit of electrical resistance, defined as the resistance between two poin](https://unitfyi.com/glossary/ohm-def/)
- [Orders of Magnitude — A way of expressing and comparing quantities using powers of 10, where each orde](https://unitfyi.com/glossary/orders-of-magnitude/)
- [Ounce — A dual-use imperial unit: as a mass unit (avoirdupois), 1 oz = 28.3495 g (1/16 l](https://unitfyi.com/glossary/ounce-def/)
- [Parsec — A unit of distance equal to about 3.26 light-years or 3.086×10¹⁶ meters.](https://unitfyi.com/glossary/parsec-def/)
- [Pascal — The SI unit of pressure, equal to one newton per square meter.](https://unitfyi.com/glossary/pascal-def/)
- [Pica — The pica is a typographic unit equal to 12 points or exactly 1/6 of an inch (app](https://unitfyi.com/glossary/pica-def/)
- [Pint — A volume unit equal to 1/2 quart: the US liquid pint is 473.176 mL; the UK imper](https://unitfyi.com/glossary/pint-def/)
- [Pixel — A pixel (picture element) is the smallest individually addressable point of colo](https://unitfyi.com/glossary/pixel-def/)
- [Planck Constant — A fundamental physical constant with the exact value 6.62607015 × 10⁻³⁴ J·s, whi](https://unitfyi.com/glossary/planck-constant-def/)
- [Point (Typography) — A unit of type size. The desktop publishing point equals 1/72 of an inch.](https://unitfyi.com/glossary/point-typography/)
- [Pound — An imperial unit of mass equal to exactly 453.59237 grams (16 avoirdupois ounces](https://unitfyi.com/glossary/pound-def/)
- [Precision — The degree of refinement in a measurement, indicated by the number of significan](https://unitfyi.com/glossary/precision/)
- [Proof (Alcohol) — Proof is a measure of alcoholic strength; in the US system, proof equals exactly](https://unitfyi.com/glossary/proof-alcohol-def/)
- [Proportionality — A mathematical relationship between two quantities where their ratio remains con](https://unitfyi.com/glossary/proportionality-def/)
- [PSI (Pounds per Square Inch) — A unit of pressure expressing force in pounds applied over one square inch.](https://unitfyi.com/glossary/psi-def/)
- [Pyeong — A Korean unit of area equal to approximately 3.3058 square meters.](https://unitfyi.com/glossary/pyeong-def/)
- [Quart — A volume unit equal to one quarter of a gallon: the US liquid quart is 946.353 m](https://unitfyi.com/glossary/quart-def/)
- [Random Error — Unpredictable, statistical variation in measurements caused by uncontrolled fact](https://unitfyi.com/glossary/random-error/)
- [Reference Standard — A measurement standard with the highest metrological quality available at a give](https://unitfyi.com/glossary/reference-standard-def/)
- [Refractive Index — The refractive index (n) of a medium is the ratio of the speed of light in a vac](https://unitfyi.com/glossary/refractive-index/)
- [Reproducibility — The closeness of agreement between independent measurement results obtained unde](https://unitfyi.com/glossary/reproducibility-def/)
- [Resolution — The smallest change in the quantity being measured that causes a detectable chan](https://unitfyi.com/glossary/measurement-resolution/)
- [Reynolds Number — The Reynolds Number is a dimensionless quantity that predicts whether fluid flow](https://unitfyi.com/glossary/reynolds-number-def/)
- [Rounding — The process of reducing the number of digits in a value while keeping it close t](https://unitfyi.com/glossary/rounding/)
- [RPM — RPM (revolutions per minute) is a unit of rotational speed measuring how many co](https://unitfyi.com/glossary/rpm-def/)
- [Scaling — The process of multiplying or dividing measurements by a consistent factor to co](https://unitfyi.com/glossary/scaling-def/)
- [Scientific Notation — A method of expressing numbers as a coefficient between 1 and 10 multiplied by a](https://unitfyi.com/glossary/scientific-notation-def/)
- [Second — The SI base unit of time, defined by the cesium-133 atom.](https://unitfyi.com/glossary/second/)
- [Shaku (尺) — The shaku (尺) is a traditional Japanese unit of length equal to 10/33 meters, ap](https://unitfyi.com/glossary/shaku-def/)
- [Significant Figures — The meaningful digits in a number that contribute to its measurement precision.](https://unitfyi.com/glossary/significant-figures/)
- [Slug — An imperial unit of mass where 1 slug accelerates at 1 ft/s² when 1 pound-force ](https://unitfyi.com/glossary/slug-def/)
- [Span — The span is an ancient unit of length equal to the width of an outstretched hand](https://unitfyi.com/glossary/span-def/)
- [Specific Gravity — The dimensionless ratio of a substance’s density to the density of a reference s](https://unitfyi.com/glossary/specific-gravity-def/)
- [Specific Heat Capacity — Specific heat capacity is the amount of energy required to raise the temperature](https://unitfyi.com/glossary/specific-heat-def/)
- [Speed of Light — The exact speed at which light travels in vacuum: 299,792,458 meters per second,](https://unitfyi.com/glossary/speed-of-light-def/)
- [Stadion — The stadion (or stade) is an ancient Greek unit of length approximately equal to](https://unitfyi.com/glossary/stadion-def/)
- [Standard Atmosphere — A reference unit of pressure defined as exactly 101,325 pascals (101.325 kPa), r](https://unitfyi.com/glossary/atmosphere-pressure-def/)
- [Standard Conditions (STP) — The IUPAC reference state for gas measurements: 0°C (273.15 K) and 101.325 kPa (](https://unitfyi.com/glossary/standard-conditions-def/)
- [Standard Gravity — The nominal gravitational acceleration at Earth’s surface, defined exactly as 9.](https://unitfyi.com/glossary/standard-gravity-def/)
- [Stick of Butter — A stick of butter is a US baking measure equal to 1/2 cup, 8 tablespoons, 1/4 po](https://unitfyi.com/glossary/stick-of-butter-def/)
- [Stone — A British unit of weight equal to 14 pounds (6.35 kg).](https://unitfyi.com/glossary/stone-def/)
- [Strain — Strain is the dimensionless ratio of a material's deformation (change in length)](https://unitfyi.com/glossary/strain-def/)
- [Stress — Stress is the internal force per unit area within a material resulting from exte](https://unitfyi.com/glossary/stress-def/)
- [Systematic Error — A consistent, repeatable deviation of measurements from the true value, caused b](https://unitfyi.com/glossary/systematic-error/)
- [Tablespoon — A cooking volume unit. The US tablespoon equals approximately 14.787 ml.](https://unitfyi.com/glossary/tablespoon-def/)
- [Talent — The talent was a unit of weight and currency in the ancient world, varying from ](https://unitfyi.com/glossary/talent-def/)
- [Teaspoon — A cooking volume unit. The US teaspoon equals approximately 4.929 ml.](https://unitfyi.com/glossary/teaspoon-def/)
- [Tensile Strength — Tensile strength is the maximum stress a material can withstand while being stre](https://unitfyi.com/glossary/tensile-strength-def/)
- [Thermal Expansion — Thermal expansion is the tendency of matter to change its volume in response to ](https://unitfyi.com/glossary/thermal-expansion-def/)
- [Throughput — Throughput is the actual rate at which data is successfully transferred over a n](https://unitfyi.com/glossary/throughput-def/)
- [Tire Size Numbers — Tire size is encoded in the format Width/AspectRatio R Diameter (e.g., 205/55 R1](https://unitfyi.com/glossary/tire-size-numbers/)
- [Tolerance — The permissible range of variation in a measurement or manufactured dimension, d](https://unitfyi.com/glossary/tolerance-def/)
- [Ton — Three distinct units: the short ton (US) = 2,000 lb (907.185 kg); the long ton (](https://unitfyi.com/glossary/ton-def/)
- [Torque — Torque is the rotational equivalent of force, equal to the applied force multipl](https://unitfyi.com/glossary/torque-def-eng/)
- [Traceability — An unbroken, documented chain of calibrations linking a measurement result to a ](https://unitfyi.com/glossary/traceability-def/)
- [Troy Weight — A system of weights used for precious metals and gemstones.](https://unitfyi.com/glossary/troy-weight/)
- [Tsubo (坪) — The tsubo (坪) is a Japanese unit of area equal to the area of two tatami mats, a](https://unitfyi.com/glossary/tsubo-def/)
- [Twip — A twip (twentieth of a point) is a typographic unit equal to 1/20 of a printer's](https://unitfyi.com/glossary/twip-def/)
- [Unit Analysis — A problem-solving technique that verifies equations and performs conversions by ](https://unitfyi.com/glossary/unit-analysis-def/)
- [Unit Symbol Rules — The BIPM conventions governing how SI unit symbols are written: upright (roman) ](https://unitfyi.com/glossary/unit-symbol-rules/)
- [Viscosity — Viscosity is a fluid's resistance to deformation or flow, quantifying internal f](https://unitfyi.com/glossary/viscosity-def/)
- [Volt — The SI unit of electric potential difference (voltage), defined as one joule of ](https://unitfyi.com/glossary/volt-def/)
- [Watt — The SI unit of power, equal to one joule per second.](https://unitfyi.com/glossary/watt-def/)
- [Wavelength — Wavelength is the distance between two consecutive identical points (such as cre](https://unitfyi.com/glossary/wavelength-def/)
- [Weight vs Volume in Cooking — Weight measurement in cooking uses mass units (grams, ounces) rather than volume](https://unitfyi.com/glossary/weight-vs-volume-cooking/)
- [X-Height — X-height is the typographic height of a typeface's lowercase letters, specifical](https://unitfyi.com/glossary/x-height-def/)
- [Yard — An imperial unit of length equal to 3 feet, 36 inches, or exactly 0.9144 meters.](https://unitfyi.com/glossary/yard-def/)

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- [Unit Comparison](https://unitfyi.com/tools/comparison/)
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