Unit Converter
Convert between units instantly — everything runs in your browser.
Common conversions
Convert length, weight, temperature and other everyday units when recipes, manuals, or travel notes use a different system from the one you think in.
Who this is for
People reading a number written for somewhere else: an American recipe in cups, a US datasheet in inches and BTU, a European parcel in kilograms, a tyre pressure in psi. It also covers the two conversions that quietly cause the most trouble in technical work — gigabytes against gibibytes, and US gallons against imperial gallons — where the two answers differ by enough to matter. If you need a legally traceable measurement for trade, calibration or dispensing, you need a certified instrument, not a web page.
The eleven categories
Length, weight and mass, temperature, area, volume, speed, time, digital storage, pressure, energy, and angle. Each category converts through a base unit — metres for length, kilograms for mass, pascals for pressure — so any unit in a category converts to any other in one step.
How to use the Unit Converter
- Pick a category from the row of tabs. The unit lists change to match it.
- Type a number in the left box and choose the unit it is currently in.
- Choose the unit you want on the right. The result updates as you type — there is no convert button.
- Press Swap to reverse the direction while keeping the value.
Worked examples
Example 1 — a US recipe in Australia. Volume, 1 US cup to millilitres, gives 236.58824 mL. Note that the tool's cup is the US cup. An Australian metric cup is 250 mL, so a recipe scaled with local measuring cups differs from this conversion by about 5 per cent — enough to notice in baking, not enough to matter in a casserole.
Example 2 — the gallon trap. Volume, 1 US gallon to litres, gives 3.7854118. Change the source unit to imperial gallon and the same "1 gallon" becomes 4.54609 L. That is a 20 per cent difference, and it is why fuel economy quoted in miles per gallon cannot be compared between American and British sources unless you know which gallon was meant.
Example 3 — why a new drive looks smaller than the box said. Digital storage, 1 TB to GiB, gives 931.32257. Drive makers sell in decimal terabytes (1 TB = 1,000,000,000,000 bytes) while Windows reports binary gibibytes. Nothing is missing — the same bytes are being counted in units of a different size. The tool lists both families (KB, MB, GB, TB alongside KiB, MiB, GiB, TiB) so you can show the difference rather than argue about it.
Example 4 — temperature is not a multiplication. Temperature, 20 °C to °F, gives 68. But 40 °C is 104 °F, not double. Celsius and Fahrenheit have different zero points, so converting multiplies and shifts. Doubling a Celsius value never doubles the Fahrenheit one, which is why temperature is handled by its own formulas here rather than by a single factor like every other category.
Common mistakes
Assuming "gallon", "ton" and "cup" mean one thing. Each appears twice in this tool with different values — US and imperial gallon, US short ton and UK long ton, US cup against the 250 mL metric cup used in Australian recipes. Read the unit label, not just the word.
Mixing decimal and binary storage units. KB and KiB are not the same size, and the gap widens as the units get bigger: about 2 per cent at kilobytes, roughly 10 per cent by terabytes.
Scaling a temperature. Converting a temperature works; multiplying one does not. "Twice as warm" has no meaning on a scale whose zero is arbitrary.
Treating month and year as exact. In the Time category a month is defined as 30 days and a year as 365. That is fine for rough durations and wrong for calendar arithmetic — it ignores month lengths and leap years entirely. For real dates, count with a calendar.
Before you start
Know which variant of your unit the source meant. Most conversion errors are not arithmetic errors — the sum is done correctly on the wrong unit. A British workshop manual quoting gallons means imperial; an American one means US. A recipe printed in Sydney means the metric cup. Once you have that right, the conversion itself is exact.
Accuracy and rounding
The conversion factors are the exact defined values, not approximations: an inch is exactly 0.0254 m, a pound exactly 0.45359237 kg, a mile exactly 1609.344 m. These are definitions rather than measurements, so there is no error to accumulate.
Results are displayed to eight significant figures. That is far finer than any everyday use needs and is where any visible imprecision comes from — the underlying arithmetic uses standard double-precision floating point, so a value like 0.1 + 0.2 can land a vanishing fraction away from a round number. It will never affect a measurement you act on.
Tips
Swap is faster than retyping. If you converted the wrong way round, press Swap rather than re-entering the number and re-picking both units.
Convert through the base unit for odd pairs. Any unit converts directly to any other inside a category, so you can go straight from arcseconds to turns, or from foot-pounds to kilowatt-hours, without stepping through a common unit yourself.
Use it to sanity-check, not just to convert. Converting 1 atm to psi (14.695949) is a quick way to confirm a gauge reading is plausible before you trust the rest of a spec sheet.
The unit names use US spellings — "Meter", "Liter", "Kilometer" — because those are the SI symbols' English forms as written in the tool. Metre and litre are the same units.
Accessibility notes
The category tabs and both unit lists are standard HTML controls, so they are reachable by Tab and operable with the arrow keys, and a screen reader announces each unit by its full name rather than its symbol — "Kilogram (kg)" rather than "kg". The result updates as you type, which means a screen reader using a live region will announce it without you having to move focus. Dark mode is available from the theme toggle.
Limitations (honest)
- Not legal for trade. Anything sold, dispensed or certified by measure needs an approved instrument. This is a reference, not a measuring device.
- Month = 30 days, year = 365 days in the Time category. No leap years, no real month lengths.
- Eight significant figures on output, and standard double-precision arithmetic underneath. Not arbitrary-precision.
- No currency, because exchange rates change by the minute and would need a live feed.
- No compound units. You cannot enter "5 ft 9 in" or convert kilometres per litre to miles per gallon in one step — convert each part separately.
- Fuel economy, torque and force are not categories. Energy covers joules, calories, watt-hours and BTU, but not power.
- Requires JavaScript in a current browser.
Privacy
Every conversion is arithmetic done in your browser. The factor table is part of the page, so once it has loaded the tool never contacts our server again — the numbers you type are not sent anywhere, not logged, and not stored. Nothing you convert is retained after you close the tab.
Advertising cookies and your choices about them are described in our Privacy Policy and the consent notice shown on your first visit.
Related tools on ToolsAre.Us
If your conversion is one step in a longer sum, the Calculator handles the arithmetic around it. Durations converted here often pair with the Stopwatch and Timer for actually measuring one, or the Countdown for a shared deadline. If you are converting times rather than durations, the World Timezones tool handles offsets and daylight saving, which no fixed factor can. The full set is on the home page.
FAQ
Is this a US gallon or an imperial gallon?
Both are available and they are listed separately. A US gallon is 3.785411784 litres; an imperial gallon is 4.54609 litres — about 20 per cent larger. The same applies to quarts and pints. If a source does not say which it means, British and Australian material written before metrication is usually imperial, and anything American is US.
What is the difference between GB and GiB?
A gigabyte is 1,000,000,000 bytes; a gibibyte is 1,073,741,824 bytes. Storage manufacturers use the decimal units, and Windows reports the binary ones while labelling them "GB", which is why a 1 TB drive shows as roughly 931 GB. Both unit families are in the Digital storage category so you can convert between them directly.
Can I use this for anything sold by weight or measure?
No. Trade measurement is regulated, and it requires an instrument that has been pattern-approved and verified — in Australia that is administered by the National Measurement Institute. This tool is a reference for working out what a number means, not a device for determining what someone owes.
How accurate is it?
The factors are exact defined values, so the conversion introduces no error of its own. An inch is defined as exactly 0.0254 metres and a pound as exactly 0.45359237 kilograms. Results show eight significant figures, computed in standard double-precision floating point — accurate far beyond any practical use, but not arbitrary-precision.
Why is a month 30 days?
Because a month has no fixed length, the Time category has to pick one, and 30 days is the common convention for approximate durations. It means the month and year units are useful for rough spans and wrong for calendar arithmetic — they ignore leap years and the real length of each month. For actual dates, count on a calendar instead.
Can it convert currency?
No. Every conversion here uses a fixed factor that never changes, which is exactly what an exchange rate is not. Adding currency would mean fetching live rates from an external service and sending your figures to it, which would break the tool's main property — that nothing you type leaves your browser.
Can I enter a compound value like 5 ft 9 in?
Not in one box. Convert the parts separately and add them, or convert the whole thing to a single unit first — 5 ft 9 in is 69 inches, which converts cleanly to 175.26 cm.
Does it work offline?
Yes, once the page has loaded. The entire factor table ships with the page, so conversions keep working with the network disconnected. The page itself has to be fetched first, and it is not installable as an offline app.
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