Free Unit Converters
Conversion tools that show the common values already worked out, and say whether each factor is exact or rounded.
Browse by category
Power and Energy
Watts through BTU, plus joules, calories and kWh, with the power versus energy distinction made clear.
Speed
m/s through Mach.
Energy
Both calories, kept apart.
Area
Square meters through square miles, including the are, which European land listings use and English converters usually leave out.
Data Storage
Bytes to petabytes, both counting conventions.
Electrical
Watts, volts, amps and ohms solved from any two, plus power factor handled properly.
Numbers and Bases
Binary, octal, decimal, hex.
Length and Distance
Millimeters through nautical miles in one tool, plus six dedicated length converters.
Weight and Mass
Milligrams to tonnes.
Temperature
C, F, K and Rankine.
Cooking and Baking
Teaspoons through gallons, plus the ingredient-specific weight tools a fixed ratio can't handle.
Pressure
Pascals to inches of mercury.
Kitchen and temperature
Celsius to Fahrenheit
Oven temperatures, gas marks and body temperature. 180 °C, 200 °C and the rest already converted.
Cups to Grams
By ingredient, because flour and honey don't weigh the same.
Kilograms to Pounds
With stones and pounds output.
Workshop and vehicle
How these tools are built
Every conversion factor on this site is taken from the NIST Guide to the SI, Appendix B, and every page states whether the factor it uses is exact by definition or rounded. That distinction matters more than it sounds: the pound is defined as exactly 0.45359237 kilograms, but the figure most converters show you, 2.2046226 pounds per kilogram, is a rounded reciprocal.
Ingredient weights for the cooking tools come from King Arthur Baking's ingredient weight chart. Where reputable sources disagree, as they do on the weight of a cup of flour, the pages say so and name the figures rather than picking one quietly.
Time, angle and more
Minutes to Hours
Hours and minutes plus decimal hours, since timesheets want one and people say the other.
Degrees to Radians
Exact multiples of pi.
Grams to Ounces
Avoirdupois and troy.
GB to TB
Why 1 TB shows as 931 GB.
Data, area, speed and volume
KB to MB
Decimal and binary conventions side by side, because ranking pages disagree with each other on this.
MB to GB
Why 32 GB shows as 29.8.
Liters to Gallons
US and imperial, both shown.
Knots to Mph
Marine and aviation speeds with the Beaufort wind scale alongside.
Kph to Mph
European speed limits.
Hectares to Acres
Land area.
Sq Ft to Sq M
Floor areas.
Length and distance
Height Converter
Centimeters to feet and inches, with the rounding boundaries shown so you know which whole inch you fall into.
Cm to Inches
With the nearest tape fraction.
Mm to Inches
Down to 1/64, error shown.
Km to Miles
Road and race distances, including why pace doesn't convert the same way.
Feet to Meters
Exact factor both directions.
Numbers and bases
Electrical and force
Guides
Sources
- NIST Guide to the SI, Appendix B: Conversion Factors. National Institute of Standards and Technology. Source for every physical conversion factor used across this site.
- Ingredient Weight Chart. King Arthur Baking. Source for the ingredient weights used by the cooking converters.
What is here, and what isn't
Forty-eight converters and eight guides are live now, organized under twelve category hubs. A few categories are deliberately absent rather than pending: currency needs live rates and would go stale, and clothing sizes are dominated by incumbents this site can't usefully compete with. Frequency, density and flow rate are simply not built yet.