Convert between any units: inches to centimeters, pounds to kilograms, Fahrenheit to Celsius, gallons to liters, miles to kilometers, and dozens more. Free instant US converter.
Essential US ↔ Metric Conversions
The US is one of three countries (with Liberia and Myanmar) still primarily using the imperial system. Understanding both systems is practically useful for travel, imported goods, scientific work, and increasingly for fitness and nutrition labels.
Category
US Unit
Metric Equivalent
Length
1 inch
2.54 cm
Length
1 mile
1.609 km
Weight
1 pound
0.454 kg
Volume
1 gallon
3.785 L
Temperature
32°F
0°C
Temperature
98.6°F
37°C
Why This Matters Financially
Unit conversions affect real money decisions. Gas mileage: a 35 MPG car getting 14.9 km/L. International shipping: rates quoted in kg affect pricing for e-commerce sellers. Real estate internationally: lots measured in hectares (1 acre = 0.405 hectares). Medical dosing: weight-based drug dosing uses kg. Fitness and nutrition: macros and serving sizes often mix metric and imperial. Getting conversions wrong in business contexts can mean significant pricing errors. For currency conversions when traveling internationally, use our Currency Converter.
Frequently Asked Questions
1 inch = 2.54 centimeters exactly (defined). Useful conversions: 1 foot = 30.48 cm; 5 feet = 152.4 cm; 6 feet = 182.88 cm. For quick mental math: multiply inches by 2.54, or multiply centimeters by 0.3937 to get inches. A 5'10" American is 177.8 cm. A 180 cm European is about 5'11". Height is one of the most common unit conversions for Americans traveling internationally.
°C = (°F − 32) × 5/9. Or: subtract 32, divide by 1.8. Key benchmarks: 32°F = 0°C (freezing); 98.6°F = 37°C (body temp); 212°F = 100°C (boiling); 68°F = 20°C (comfortable room temp). Quick reverse estimate: double the Celsius, subtract 10% of that, add 32. So 25°C: double = 50, minus 5 = 45, plus 32 = 77°F. This gives about ±2°F accuracy for everyday temperatures.
1 kilogram = 2.20462 pounds. For quick math, multiply kg by 2.2 to get pounds, or divide pounds by 2.2 to get kg. A 150 lb American weighs about 68 kg. A 70 kg package weighs about 154 lbs. For body weight: divide pounds by 2.2. Most gym equipment in the US shows pounds; most pharmaceutical dosing uses kg (drugs are often dosed at X mg per kg of body weight).
1 kilometer = 0.621371 miles. 1 mile = 1.60934 kilometers. For quick math: km × 0.6 ≈ miles (slight underestimate); miles × 1.6 ≈ km. A 5K race is 3.1 miles. A marathon (26.2 miles) is 42.2 km. Speed: 60 mph = 96.6 km/h; 100 km/h = 62.1 mph. For rental cars in Canada or Europe: 120 km/h speed limit = about 75 mph. The kilometer estimate shortcut: multiply km by 6, drop the last digit.
1 US gallon = 3.785 liters. 1 liter = 0.264 US gallons. A standard water bottle (16.9 oz) is 0.5 liters. A full bathtub holds about 40–50 gallons (150–190 liters). Gas/petrol: US pumps in gallons; most of the world uses liters. If gas costs $3.50/gallon in the US and €1.80/liter in Europe, converting: €1.80 × 3.785 = €6.81/gallon equivalent — roughly 94% more expensive per gallon in Europe before currency conversion.
