Conversion
Unit Converter
Convert between common metric and imperial units using exact international conversion factors.
- Choose a measurement type.
- Pick the from and to units.
- Enter a value.
How it works
Each unit is stored with its exact size in a base unit, such as metres for length or kilograms for weight. To convert, the calculator multiplies your value by the size of the starting unit and divides by the size of the target unit, so every pair of units is converted the same reliable way.
Temperature is different because the scales have different zero points, so the calculator uses the proper formulas for Celsius, Fahrenheit and Kelvin. It rejects temperatures below absolute zero. You can swap the units with one click to convert back.
Results are shown with sensible rounding for everyday use, while the calculation itself keeps full precision until the end. This matters when converting large numbers or converting back and forth, because rounding at each step can slowly add errors. Supported groups are length (millimetres to miles), weight (milligrams to tonnes, plus pounds and ounces), temperature (Celsius, Fahrenheit and Kelvin) and volume (millilitres to US and UK gallons). Only units from the same group can be paired, which stops impossible conversions such as kilograms to litres.
Formula
Result = Value × (From factor ÷ To factor)
°F = °C × 9/5 + 32
K = °C + 273.15
Worked examples
100 °C → (100 × 9/5) + 32 = 212 °F.
Running distance
10 km = 10 × 1,000 ÷ 1,609.344 = 6.21 miles.
Body weight
70 kg = 70 ÷ 0.45359237 = 154.32 lb.
Oven temperature
180 °C = 180 × 9/5 + 32 = 356 °F.
Understanding the result
Only units of the same type can be converted, so you can't accidentally turn kilograms into metres. Factors follow international definitions, e.g. 1 inch = 2.54 cm exactly, 1 lb = 0.45359237 kg.
Common mistakes
- Mixing up US and UK gallons, which differ by about 20%.
- Converting temperatures by multiplying only, forgetting the +32 offset for Fahrenheit.
- Confusing fluid ounces (volume) with ounces (weight).
- Rounding too early in a multi-step calculation.
When to use it
- Following recipes from other countries.
- Understanding distances, speeds, and fuel amounts when travelling.
- Converting body weight or height for forms.
- Checking product sizes when shopping online.
FAQs
- Are US and UK gallons the same?
- No. A US gallon is 3.785 L; a UK (imperial) gallon is 4.546 L. Both are listed separately.
- Why can't I enter −300 °C?
- It's below absolute zero (−273.15 °C), which isn't physically possible.
- How accurate are the conversions?
- They use exact international definitions, such as 1 inch = 2.54 cm and 1 lb = 0.45359237 kg.
- Can I convert weight to volume?
- No. That depends on the density of the material, so only units of the same type can be converted.
- What is Kelvin?
- A temperature scale that starts at absolute zero. 0 °C equals 273.15 K.
- How many centimetres are in a foot?
- Exactly 30.48 centimetres, because a foot is 12 inches and each inch is exactly 2.54 centimetres. That makes a common height of 5 feet 10 inches equal to 177.8 centimetres.
- How do I convert stones to kilograms?
- A stone is 14 pounds. Multiply the stones by 14, then convert those pounds to kilograms here; 11 stone is 154 lb, or about 69.85 kg.
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