Free Unit Converter
Convert between metric and imperial units for length, weight, and temperature.
How to use / FAQ
Pick a category — length, weight, or temperature — type a value, and choose the units to convert between. The result updates live, and the swap button flips the two units so you can reverse the conversion in one click.
Most unit conversions come down to a handful of everyday situations: a recipe in ounces when your scale reads grams, a race distance in kilometres when you think in miles, a weather forecast in Fahrenheit when you know Celsius, furniture measured in centimetres for a room you measured in feet. Rather than memorising factors, type the number you have and read off the number you need — the conversion uses exact, internationally agreed definitions, so the answer is as accurate as the measurement you started with.
Which units are supported?
Length covers millimeters through miles (metric and imperial), weight runs from milligrams to metric tons plus ounces, pounds, and stone, and temperature handles Celsius, Fahrenheit, and Kelvin.
What are the most useful factors to remember?
A few cover most daily needs: 1 inch = 2.54 cm, 1 foot = 30.48 cm, 1 mile ≈ 1.609 km, 1 kg ≈ 2.205 lb, 1 ounce ≈ 28.35 g, and 1 stone = 14 lb ≈ 6.35 kg. For everything else, that's what this page is for.
How do I convert Celsius to Fahrenheit in my head?
Exactly: multiply by 9/5 and add 32. Roughly: double it and add 30 — good enough for weather (20°C ≈ 70°F; the exact answer is 68°F). Going the other way, subtract 30 and halve it. Handy anchors: 0°C = 32°F, 10°C = 50°F, 37°C = 98.6°F (body temperature), 100°C = 212°F.
Why is temperature handled differently?
Temperature scales have offsets, not just different sizes, so a simple multiply won't do — 0°C isn't 0°F. The tool converts through Celsius to get exact results, including negative values and Kelvin's absolute scale.
What is a stone, and where is it used?
A stone is a British and Irish unit of body weight equal to 14 pounds, or about 6.35 kg. Someone who weighs '11 stone 4' weighs 11 × 14 + 4 = 158 lb, roughly 71.7 kg. It's rarely used outside body weight.
When would I use Kelvin?
Kelvin is the scientific temperature scale: it starts at absolute zero (−273.15°C), so it has no negative values. A kelvin step is the same size as a Celsius degree — just add 273.15 to °C. Room temperature is about 293 K; you'll meet Kelvin in physics, chemistry, and colour temperature of light.
How do I reverse a conversion?
Use the swap button between the two unit menus — it flips From and To in one click, turning meters-to-feet into feet-to-meters without re-picking anything.
How precise are the results?
Conversions use exact standard factors (for example, 1 inch is defined as exactly 0.0254 m) and display up to eight significant digits. Any rounding you see at the end of a long decimal is display rounding, not an approximation in the maths.