Unit Converter
Convert between metric and imperial units for length, weight, volume, and temperature using exact internationally-defined factors (1 inch = 2.54 cm exactly, 1 lb = 0.45359237 kg exactly). Pick a unit to convert from and to — the converter keeps you within the same dimension and tells you if you try to mix, say, mass and length.
When to use this calculator
- Converting miles to kilometers (or back) for travel and running
- Switching a recipe between US cups/ounces and metric ml/grams
- Converting body weight between kilograms and pounds
- Reading a thermostat or recipe in the other temperature scale
- Converting heights and distances between feet/inches and centimeters
- Checking a product spec given in unfamiliar units
How it works
1 min readWhat is a unit converter?
It converts a value from one unit of measure to another within the same physical dimension — length, mass (weight), volume, or temperature — using standardized conversion factors.
How It Works
For length, mass, and volume, every unit is defined relative to a base unit (meter, kilogram, liter). The value is converted to the base unit, then to the target unit: result = value × fromFactor ÷ toFactor. Temperature uses offset formulas instead of simple factors, because the scales don't share a zero point.
Key Factors (exact by definition)
1 inch = 2.54 cm 1 mile = 1609.344 m
1 foot = 0.3048 m 1 yard = 0.9144 m
1 pound = 0.45359237 kg 1 oz = 28.349523 g
1 US gal = 3.785412 L 1 US cup = 236.588 mLTemperature Formulas
°C → °F: F = C × 9/5 + 32
°F → °C: C = (F − 32) × 5/9
°C → K: K = C + 273.15Worked Examples
| Convert | Result |
|---|---|
| 1 mile → km | 1.609344 km |
| 1 kg → lb | 2.204623 lb |
| 100 °C → °F | 212 °F |
| 1 US gallon → liters | 3.785412 L |
Limitations
Frequently asked questions
How many kilometers is a mile?
1 mile equals exactly 1.609344 kilometers. So 5 miles = 8.04672 km, and to go the other way, 1 km = 0.621371 miles. The conversion is exact by international definition.
How do I convert kg to pounds?
Multiply kilograms by 2.204623 to get pounds (1 kg = 0.45359237 kg per pound, inverted). So 70 kg = 154.3 lb. To convert pounds to kg, multiply by 0.453592.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32: F = C × 1.8 + 32. So 100 °C = 212 °F (boiling point) and 0 °C = 32 °F (freezing). To reverse: C = (F − 32) × 5/9.
Are US and UK gallons the same?
No. A US gallon is 3.785412 liters; an imperial (UK) gallon is 4.546092 liters — about 20% larger. This converter uses US liquid measures for gallons, quarts, pints, cups, and fluid ounces.
Why can't I convert kilograms to meters?
Because they measure different physical dimensions — mass versus length. Unit conversion only works within the same dimension. The calculator detects a cross-dimension attempt and returns an explanatory error instead of a meaningless number.
How do I convert cups to grams?
You can't with a pure unit converter — cups measure volume and grams measure mass, so the conversion depends on the ingredient's density (a cup of flour and a cup of sugar weigh different amounts). Use an ingredient-specific cooking converter for that.
What is the exact definition of an inch?
Since 1959, one inch is defined as exactly 2.54 centimeters. From this, a foot is 0.3048 m and a mile is 1609.344 m — all exact. That's why this converter's length results are precise rather than rounded approximations.
How precise are the results?
Results use exact internationally-defined factors and are shown to up to 6 significant decimals. For everyday use you can round; for engineering or scientific work, the underlying factors are exact and suitable for further calculation.