Calculation & Conversion / Converters
Unit Converter
A unit converter changes a measurement from one unit to another within the same category — length, weight, temperature, area, volume, speed, data storage or time — and shows the result instantly as you type. Every factor is the exact international definition, such as 1 inch = 2.54 cm and 1 pound = 0.45359237 kg, so the arithmetic is exact within double precision rather than rounded to a rough rule of thumb. The whole calculation runs in your browser and nothing you enter is uploaded.
This space is reserved for a sponsor. Every tool on this site stays free and runs locally in your browser.
This space is reserved for a sponsor. Every tool on this site stays free and runs locally in your browser.
How to use
- 1
Pick a category
Choose Length, Weight & Mass, Temperature, Area, Volume, Speed, Data Storage or Time. The source and target units reset to the most common pair for that category, such as cm to inches.
- 2
Choose the units
Set the From and To units from the two dropdowns. Use the swap button to exchange them; if you pick the same unit on both sides the other one is moved automatically so they never collide.
- 3
Type the value
Enter a number and the result updates as you type — there is no convert button. Commas in large numbers are accepted, and negative values work for temperature.
- 4
Read the result
The converted value is shown to ten significant digits next to the target unit symbol, with the full equation underneath so you can see exactly what was computed.
- 5
Use the reference table
Below the result, a table converts your value into every unit in the category at once, so you can compare metric and imperial side by side. Copy the main result with one click.
Key facts
- One inch is exactly 2.54 cmSince the 1959 international yard and pound agreement, the inch is defined as exactly 2.54 centimetres. The value is a definition, not a measurement, so converting inches to centimetres is exact — for example 12 inches is exactly 30.48 cm.Source:International yard and pound agreement (1959); NIST Handbook 44
- 0 °C equals 32 °FThe Celsius scale is anchored at the freezing point of water, 0 °C, which equals 32 °F, and the boiling point, 100 °C, which equals 212 °F. The conversion is F = C × 9/5 + 32; modern definitions fix the kelvin so that 0 °C is exactly 273.15 K.Source:SI Brochure (BIPM); NIST Special Publication 811
Frequently asked questions
How accurate is the conversion?
It is as accurate as the numbers allow. Every factor is the exact international definition — 1 inch is exactly 0.0254 m, 1 pound is exactly 0.45359237 kg, 1 mile is exactly 1609.344 m — so a conversion is a single multiply and divide in double precision, not a rounded rule of thumb. Results are displayed to ten significant digits, with trailing zeros removed, and very large or very small values switch to scientific notation. Temperature uses affine formulas rather than a ratio because the scales have different zero points.
Which unit categories are supported?
Eight: length (metre, kilometre, centimetre, millimetre, mile, yard, foot, inch, nautical mile and more), weight and mass (kilogram, gram, pound, ounce, stone, metric ton, US ton), temperature (Celsius, Fahrenheit, Kelvin), area (square metre, hectare, acre, square foot, square inch), volume (litre, millilitre, US gallon, quart, pint, cup, fluid ounce, tablespoon, teaspoon, imperial gallon), speed (metre per second, kilometre per hour, mile per hour, knot, foot per second), data storage (bit, byte, kilobyte through petabyte) and time (millisecond through year).
Can I add my own custom units?
No — and the reason is that a conversion is only meaningful when the factor is defined. Every unit here carries an exact factor against its category's base unit, so the maths is unambiguous. You are not limited in practice, though: within a category you can set any source and any target, and the reference table at the bottom converts your value into every unit in the category at once, so you can read all of them side by side.
Why does data storage use 1024 instead of 1000?
Data storage is shown in binary multiples, where 1 KB = 1024 bytes, 1 MB = 1024 KB and so on, because that is how memory and most operating systems report file sizes. The decimal version (1 kB = 1000 bytes) is used by storage manufacturers and some network standards. This tool uses the binary convention throughout; if you need the decimal value, remember that 1,000,000,000 bytes equals 1 GB in decimal but about 0.931 GB in binary.
Why might the result differ slightly from another calculator?
Small differences almost always come from rounding on the display side, not the maths. This tool keeps the full double-precision value internally and rounds only what it prints, to ten significant digits, so it will not drift. A few time units are inherently averages: the month is defined here as 30.44 days and the year as 365.25 days, the mean Gregorian year, so results involving months or years are averages rather than calendar-exact values.
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This space is reserved for a sponsor. Every tool on this site stays free and runs locally in your browser.