The Traveler's Unit Conversion Pocket Guide

Distance and Speed (km vs miles, km/h vs mph)

The single most disorienting measurement switch for US travelers abroad — and for foreign visitors to the US — is road distance and speed. Most of the world uses kilometers and km/h; the US, UK, and a handful of other countries use miles and mph.

Exact conversion factors: - 1 mile = 1.60934 km - 1 km = 0.62137 miles - 60 mph = 96.56 km/h - 100 km/h = 62.14 mph - 120 km/h = 74.56 mph

Mental math shortcuts:

The most useful approximation is the Fibonacci relationship: consecutive Fibonacci numbers (5, 8, 13, 21, 34, 55, 89) are close approximations of the miles-to-km conversion. 5 miles ≈ 8 km. 8 miles ≈ 13 km. 13 miles ≈ 21 km. 50 miles ≈ 80 km.

For speed limits: European motorways typically post 130 km/h (81 mph). Urban limits of 50 km/h = 31 mph. A UK motorway limit of 70 mph = 113 km/h.

The speed converter handles all common speed units including knots (used in aviation and maritime: 1 knot = 1.852 km/h = 1.151 mph).

Temperature (°C vs °F Quick Mental Math)

The exact formula °F = (°C × 9/5) + 32 is hard to use mentally. Two faster methods:

Method 1 — Double and add 30: °C × 2 + 30 ≈ °F (accurate to within 2° across the range you'll encounter as a traveler) - 20°C → 40 + 30 = 70°F (actual: 68°F) - 30°C → 60 + 30 = 90°F (actual: 86°F) - 10°C → 20 + 30 = 50°F (actual: 50°F — exact)

Method 2 — Anchor points to memorize: - 0°C = 32°F (freezing) - 10°C = 50°F (cold) - 20°C = 68°F (room temperature) - 28°C = 82°F (beach weather) - 37°C = 98.6°F (body temperature) - 40°C = 104°F (very hot, dangerous prolonged exposure)

For packing purposes: weather apps will tell you the forecast in local units. In Celsius, below 10°C means a coat; above 25°C means summer clothing. In Japan, 35°C+ days are declared heat advisories; in Australia, 40°C summer days in inland cities are normal.

The Celsius to Fahrenheit converter handles exact conversions for all values.

Weight (kg vs lb for Luggage Limits)

Airlines publish baggage allowances in kilograms in most of the world and in pounds in the US. Converting quickly matters at check-in.

Exact factor: 1 kg = 2.20462 lb

Practical approximation: 1 kg ≈ 2.2 lb

Standard economy baggage limits: 20–23 kg (44–50 lb) for checked bags on most international carriers. Carry-on limits are typically 7–10 kg (15–22 lb), though enforcement varies.

For body weight: European doctors will record your weight in kg. If you know your weight in pounds, divide by 2.2. A person who weighs 154 lb weighs 70 kg; 176 lb = 80 kg; 220 lb = 100 kg.

The kilogram to pound converter covers all weight conversions in both directions.

Volume (Liters vs Gallons for Fuel)

Fuel is sold by the liter in almost every country outside the US. Fuel prices posted on forecourt signs will look dramatically different — not because fuel is cheaper, but because liters are smaller than gallons.

Exact conversions: - 1 US gallon = 3.78541 liters - 1 Imperial gallon (UK) = 4.54609 liters - 1 liter = 0.26417 US gallons = 0.21997 Imperial gallons

Fuel economy: - US: miles per gallon (mpg) - EU, most of world: liters per 100 km (L/100 km) - UK: miles per gallon, but often Imperial gallons

To convert US mpg to L/100 km: divide 235.21 by the mpg value. - 30 mpg = 7.84 L/100 km - 40 mpg = 5.88 L/100 km - 50 mpg = 4.70 L/100 km

A rental car labeled "6.5 L/100 km" is approximately 36 mpg — a reasonably fuel-efficient small European car.

The gallon to liter converter handles US gallons, Imperial gallons, and liters.

Clothing and Shoe Sizes (US/UK/EU Tables)

Clothing and shoe sizes are among the most variable and least standardized measurements in everyday life. There is no universal formula — each system was developed independently, and even within systems, brands vary. The tables below are reliable starting points; always check fit before purchasing.

Women's clothing sizes:

Men's shirt sizes (chest circumference):

Shoe sizes:

EU shoe sizes are based on Paris points (⅔ of a centimeter per size). Foot length in centimeters ÷ 0.667 = approximate EU size. For a 27 cm foot: 27 / 0.667 ≈ 40.5 EU.

Cooking Measures When Abroad (US Cups vs Metric)

US recipes use volume for dry ingredients (cups, tablespoons, teaspoons). Most of the world measures dry ingredients by weight. This matters because a "cup of flour" weighs between 120–150 g depending on how tightly it is packed — a 25% variation that can ruin a recipe.

Volume conversions: - 1 US cup = 236.59 mL - 1 tablespoon (US) = 14.79 mL ≈ 15 mL - 1 teaspoon (US) = 4.93 mL ≈ 5 mL - 1 fl oz (US) = 29.57 mL

Common baking ingredient weights per US cup:

If a European recipe calls for 250 g of flour, that is approximately 2 cups (loosely scooped) or 1.7 cups (spooned and leveled). Using a kitchen scale, available for under $15, eliminates this ambiguity entirely.

UK tablespoons are also slightly larger than US ones (17.76 mL vs 14.79 mL), a difference that matters in baking but rarely in cooking.

Electrical Units (Voltage, Plug Types by Region)

Electrical compatibility is a safety issue, not just a convenience issue. Using a device rated for 120V on a 230V outlet without a transformer can damage the device or cause a fire.

Voltage by region: - 120V, 60Hz: United States, Canada, Mexico, most of Central America - 220–240V, 50Hz: Europe, Africa, Asia, Australia, most of South America - 100V, 50/60Hz: Japan

Checking your device: Look for a label on the power adapter or device itself. "Input: 100–240V, 50/60Hz" means the device is universal and only needs a plug adapter (not a voltage converter). This is common for laptops, phone chargers, and cameras. Single-voltage devices (e.g., "Input: 120V only") need a transformer when traveling to 230V countries.

Common plug types:

Multi-region travel adapters cover most combinations but do not convert voltage. For devices that are not dual-voltage, carry a step-down converter (230V → 120V) rather than risking damage.

Printable Pocket Reference Card

The following key conversions cover 90% of travel situations:

Distance: 1 mile = 1.6 km | 1 km = 0.62 miles Speed: 100 km/h = 62 mph | 60 mph = 97 km/h Temperature: °C × 2 + 30 ≈ °F | 0°C=32°F | 20°C=68°F | 37°C=98.6°F Weight: 1 kg = 2.2 lb | 23 kg = 50.7 lb (luggage limit) Fuel: 1 US gal = 3.785 L | 1 L = $0.26 gal Volume: 1 cup = 237 mL | 1 tbsp = 15 mL | 1 fl oz = 30 mL Shoe size: EU size − 31 ≈ US Men's | EU − 30 ≈ US Women's

For any conversion not covered here, the speed, temperature, weight, and volume converters are optimized for quick mobile lookup.