Unit converter
Convert length, weight, temperature and volume.
How to use the unit converter
- Pick a category: length, weight/mass, temperature or volume. The From and To menus repopulate with that category's units, first two preselected.
- Type a value — conversion runs on every keystroke, no button to press.
- Choose the From unit (what you have) and To unit (what you want); to flip a conversion, swap the two menus.
- Read the result, shown to at most 6 decimal places with the unit spelled out —
5miles gives8.04672 kilometre. - Switching category resets the unit menus, so glance at them before reading a result if you've been hopping between length and weight.
Common uses
- Cook from a US recipe with metric kit: 1 US cup is 236.588 ml (call it 237), a tablespoon about 14.8 ml, and a 350 °F oven is 176.7 °C.
- DIY and lumber: convert an 8-foot board to 2.4384 m, or a metric plan's millimetres back to inches before cutting.
- Travel math — 5 miles is 8.05 km, and the forecast in °F makes sense again in °C.
- Body weight for forms and gyms: 10 stone is 63.5 kg, and 100 g is about 3.53 oz for postage or portions.
- Science homework: Celsius ↔ Kelvin uses the exact 273.15 offset, not an approximation.
Tips & limitations
- The volume units are US customary — no UK imperial measures. A UK pint is 568 ml versus the US 473 ml, and UK gallons are about 20% bigger, so British recipe conversions will be off if you assume they match.
- Length factors are exact by definition (an inch is exactly 25.4 mm); weight and volume factors are standard values rounded to about six significant figures — plenty for cooking and shipping, not for lab metrology.
- Tonne means the metric tonne, exactly 1,000 kg — not the US short ton (about 907 kg) or the UK long ton.
- Results cap at 6 decimal places, so extreme jumps can display as 0 — 1 milligram in tonnes, for instance. Convert in two hops via a middle unit for those magnitudes.
- Temperature accepts any number, even physically impossible ones below absolute zero (−273.15 °C) — sanity-check unusual inputs yourself.
How it's built & why it's safe
Each category keeps a table of fixed factors relative to a base unit — metres for length, kilograms for weight, litres for volume — so any conversion is one multiply and one divide: value × factor(from) ÷ factor(to). Temperature can't work that way (its scales have different zero points), so Celsius, Fahrenheit and Kelvin go through the exact textbook formulas instead. Results are rounded to six decimals and formatted with your locale's separators. It's a single vanilla-JavaScript file with no lookups and no network: it works offline once loaded, and nothing you enter is stored or sent.
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Frequently asked questions
Which units are included?
Length: millimetre, centimetre, metre, kilometre, inch, foot, yard and mile. Weight: milligram, gram, kilogram, tonne, ounce, pound and stone. Volume: millilitre, litre, cubic metre, plus US teaspoon, tablespoon, cup, pint and gallon. Temperature: Celsius, Fahrenheit and Kelvin.
Are the pints, gallons and cups US or UK measures?
US customary only, and it matters: a UK imperial pint is 568 ml against the US 473 ml, a UK gallon about 4.55 litres against 3.785, and Australian metric cups are 250 ml against the US 236.588. For UK measures, convert via millilitres from another source.
How accurate are the conversions?
Length and temperature are exact — the inch, foot, yard and mile are defined in metric terms, and the temperature formulas are the textbook ones. Ounces, pounds, stone and US volumes use standard factors rounded to roughly six significant figures, far more precision than everyday use needs.
Why does my conversion show 0?
The display rounds to six decimal places, so anything smaller than 0.0000005 shows as zero — converting 1 milligram to tonnes, for example. Step through an intermediate unit (milligrams to grams, then grams to tonnes) to keep digits visible.
Is the tonne the same as a ton?
Not quite. The tonne here is the metric tonne, exactly 1,000 kg. A US short ton is 2,000 pounds (about 907 kg) and a UK long ton 2,240 pounds — neither is included, so convert tons via pounds.
Does it need an internet connection?
Only to load the page. All factors live in the script itself — no conversion API, nothing fetched, nothing you type sent anywhere — so it keeps working offline.