How to use the unit converter
Pick a measurement type (length, weight, temperature, volume, area or speed), enter the number and choose the unit you have and the unit you want. The big result is your answer; the table lists the same amount in every other unit of that type, which is handy when a recipe, a plan or a product label mixes systems.
The exact definitions behind the numbers
Imperial and US units are defined in metric terms, so most conversions are exact, not approximate:
- 1 inch = 2.54 cm exactly, so 1 foot = 30.48 cm and 1 mile = 1,609.344 m (international yard and pound agreement, 1959).
- 1 pound = 0.45359237 kg exactly; 1 ounce is 1/16 of that, and 1 stone is 14 pounds.
- 1 US gallon = 231 cubic inches = 3.785411784 L. The UK (imperial) gallon is larger: 4.54609 L. A US cup is 1/16 of a US gallon (about 236.6 mL).
- 1 acre = 43,560 square feet ≈ 4,046.86 m²; 1 hectare = 10,000 m² ≈ 2.471 acres.
- 1 nautical mile = 1,852 m, and a knot is one nautical mile per hour.
Temperature is a formula, not a factor
Celsius and Fahrenheit have different zero points, so you cannot simply multiply. Use °F = °C × 9/5 + 32 and °C = (°F − 32) × 5/9; Kelvin is Celsius plus 273.15. Example: a fever of 101.3 °F is (101.3 − 32) × 5/9 = 38.5 °C. The two scales meet at −40, where −40 °C = −40 °F.
Common conversions at a glance
| From | To | Multiply by |
|---|---|---|
| Centimeters | Inches | 0.3937 |
| Kilometers | Miles | 0.62137 |
| Kilograms | Pounds | 2.20462 |
| Liters | US gallons | 0.26417 |
| Square meters | Square feet | 10.7639 |
| km/h | mph | 0.62137 |
Quick mental shortcuts: double the kilograms and add 10% for pounds (70 kg → 140 + 14 = 154 lb); multiply kilometers by 0.6 for miles (10 km ≈ 6 mi).
Precision
Results are shown to seven significant digits, which is more than any kitchen scale, tape measure or speedometer can read. Round to what makes sense for your task — a room measured to the nearest centimeter does not need its area in square feet to four decimals. For room areas from several walls, use the square footage calculator.
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54 cm. To convert centimeters to inches, divide by 2.54 (or multiply by 0.3937): 170 cm is about 66.9 inches, or 5 feet 6.9 inches.
How do I convert kg to lbs?
Multiply kilograms by 2.20462. For example, 70 kg × 2.20462 = 154.3 lb. To go from pounds to kilograms, multiply by 0.45359237.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (1.8) and add 32. 25 °C × 1.8 + 32 = 77 °F. Going back, subtract 32 and multiply by 5/9.
Is a UK gallon the same as a US gallon?
No. A UK (imperial) gallon is 4.54609 liters and a US gallon is 3.785411784 liters, so the UK gallon is about 20% larger. Fuel-economy figures in mpg are not comparable between the two without converting.
How many square feet are in a square meter?
One square meter is 10.7639 square feet, because a meter is 3.28084 feet and area uses the square of that factor.
Last updated: October 9, 2026