Unit converters that show the working, not just the number
Ten converters for length, weight, temperature, volume, area, speed, pressure, data, angles and Roman numerals. Type a value, see the answer instantly, and see the conversion factor that produced it.
A converter that returns a bare number asks you to trust it. That is fine until the answer looks wrong and you have no way to tell whether you mistyped, picked the wrong unit, or hit one of the genuine traps — US against imperial gallons, fluid ounces that differ by about four per cent, or tons that come in three different sizes.
So each converter here shows the factor it applied alongside the result. It takes no extra time to read and it turns a black box into something you can check, which matters when the number is going into a recipe, a shipping form or a spec sheet.
No tool matches that.
Everyday
- Length Converter
Convert between millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles.
- Weight Converter
Convert between milligrams, grams, kilograms, metric tonnes, ounces, pounds, and stone.
- Temperature Converter
Convert between Celsius, Fahrenheit, and Kelvin instantly, both directions.
- Volume Converter
Convert between milliliters, liters, cubic meters, US gallons, quarts, pints, cups, and fluid ounces.
- Area Converter
Convert between square meters, square feet, acres, hectares, square kilometers, and square miles.
- Roman Numeral Converter
Convert any number to Roman numerals, or decode a Roman numeral back to a number.
Science & Engineering
- Speed Converter
Convert between kilometers per hour, miles per hour, meters per second, and knots.
- Pressure Converter
Convert between pascals, kilopascals, bar, PSI, and atmospheres.
- Data Storage Converter
Convert between bits, bytes, and the decimal (KB/MB/GB) and binary (KiB/MiB/GiB) size prefixes correctly.
- Angle Converter
Convert between degrees, radians, and gradians.
From the blog
Where conversions usually go wrong
Volume is the worst offender. A US gallon is about 3.785 litres and an imperial gallon about 4.546, a gap of roughly twenty per cent, and both are called a gallon. Fluid ounces differ too, which is why a recipe converted with the wrong assumption comes out subtly wrong rather than obviously wrong.
Weight has the same problem with tons: a short ton, a long ton and a metric tonne are three different masses. The converter names which one it is using rather than leaving you to guess from context.
Temperature is the one people try in their heads and get wrong, because it is the only common conversion with an offset as well as a factor. Celsius to Fahrenheit is not a multiplication, which is why the shortcut approximations drift badly at the ends of the range.
Precision and rounding
Results are calculated at full floating-point precision and displayed to a sensible number of significant figures, so you get a usable answer rather than fourteen decimal places of noise. The underlying value is exact where the definition is exact — an inch is defined as precisely 25.4 millimetres, not approximately.
Everything runs in your browser and nothing you type is sent anywhere, which is also why the answer appears as you type rather than after a page reload.
Common questions
US gallons or imperial gallons?
Both, selected explicitly rather than guessed from your location. The difference is around twenty per cent, so a converter that silently picks one is a converter that is silently wrong for half its users.
How many decimal places do the results use?
Enough to be useful and not so many that the number becomes unreadable, adjusted to the magnitude of the result. The calculation itself always runs at full precision; only the display is rounded.
Why does my recipe conversion look slightly off?
Almost always the ounce. A US fluid ounce is about 29.57 ml and an imperial fluid ounce about 28.41, so a recipe converted with the wrong one is close enough to look plausible and wrong enough to matter in baking. Check which system the original recipe used.
Do you convert Roman numerals both ways?
Yes, in both directions, following the standard subtractive notation where IV is four rather than IIII. It handles values up to 3,999, which is the ceiling of conventional Roman numeral notation.
Is there a limit on how many conversions I can do?
No. Everything runs locally in your browser, so there is no rate limit, no account and no daily cap.