Scientific

Unit Converter

Convert between length, weight, temperature, area, volume, and speed units instantly. Includes a full conversion table for every supported unit.

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How Unit Conversion Works

Unit conversion is the process of expressing a measurement in a different unit while preserving its value. All conversions involve multiplying or dividing by a conversion factor — a ratio that equals exactly 1 because both numerator and denominator represent the same quantity in different units.

For example: 1 inch = 2.54 cm, so to convert 5 inches to centimetres: 5 × 2.54 = 12.7 cm. To convert back, divide: 12.7 ÷ 2.54 = 5 inches.

Temperature conversions are non-linear and require formulas instead of simple multiplication: °F = (°C × 9/5) + 32 and °C = (°F − 32) × 5/9.

Metric vs. Imperial System — Key Differences

The metric system (SI) is used by most of the world and is based on powers of ten, making conversions within the system simple (e.g., 1 km = 1,000 m = 100,000 cm). The imperial system (used primarily in the United States, with some usage in the UK) uses historically derived units with less regular conversion factors (12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile).

Most Common Conversions — Quick Reference

  • Length: 1 inch = 2.54 cm | 1 foot = 30.48 cm | 1 mile = 1.609 km | 1 metre = 3.281 feet
  • Weight: 1 kg = 2.205 lbs | 1 lb = 453.6 g | 1 stone = 6.35 kg
  • Temperature: 0°C = 32°F | 100°C = 212°F | 37°C = 98.6°F (body temperature)
  • Volume: 1 litre = 4.227 US cups | 1 US gallon = 3.785 litres

Who Uses Unit Converters?

  • Cooking: Converting recipe measurements between cups, millilitres, ounces, and grams
  • Travel: Converting kilometres to miles, Celsius to Fahrenheit, kilograms to pounds
  • Science and engineering: Ensuring consistency of units across calculations
  • Construction: Converting between metric and imperial measurements
  • International trade: Converting weights, volumes, and dimensions for shipping

Frequently Asked Questions

How accurate is the unit converter?
Conversions use exact or high-precision coefficients (e.g., 1 mile = 1609.344 metres exactly by international definition). Results are displayed to up to 8 significant figures. For scientific work, validate against primary reference standards.
Which temperature formula is used?
Standard formulas: °C to °F = (°C × 9/5) + 32. °C to Kelvin = °C + 273.15. Kelvin is the SI base unit for thermodynamic temperature and is always positive.
Can I convert very large or very small numbers?
Yes. The converter automatically switches to scientific notation (e.g., 3.5e-9) for very small results, keeping the display readable regardless of magnitude.
What does the swap button do?
The swap button instantly reverses the from/to unit selection and recalculates. Useful when you want the reverse conversion — e.g., switch from "miles to km" to "km to miles" instantly.