Unit Converter — Length, Weight, Temperature & More
Convert length, mass, volume, temperature and more. Most conversions are one fixed ratio; temperature needs an offset, which is where mistakes happen.
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Most conversions are one fixed number
For length, mass, volume and almost everything else, converting means multiplying by a ratio that never changes. And many of those ratios are not measurements at all but definitions: an inch is defined as exactly 25.4 millimetres, and a pound as exactly 0.45359237 kilograms.
That is a nicer fact than it sounds. Those conversions are not approximations that could be refined by better instruments — they are exact by agreement, and they will not change.
Temperature is the exception, and it is where mistakes live
Celsius and Fahrenheit differ in both the size of a degree and the position of zero. So converting needs a multiplication and an offset, which makes it unlike every other conversion on the page.
The consequence people get wrong: you cannot convert a temperature difference the way you convert a temperature. A rise of 10 degrees Celsius is a rise of 18 degrees Fahrenheit, not 50. The offset locates a point on the scale; it has no business being applied to a change between two points.
Three anchors make the relationship concrete. Freezing is 0 Celsius and 32 Fahrenheit. Boiling is 100 and 212. And the two scales cross at minus 40, which is the only temperature that reads the same number on both.
Kelvin is the instructive middle case: it shares Celsius's degree size but not its zero, so Celsius to Kelvin is an offset with no multiplication at all. Which shows the two components are genuinely separate rather than a package.
The gallon problem
A US gallon and an imperial gallon are different sizes, the imperial one being larger. So a recipe or a fuel figure means different things depending on which country wrote it, and the word gives you no warning.
Worse, it propagates into derived units. Miles per gallon is not comparable between the two systems even though the phrase is identical — a car rated in imperial gallons looks more efficient than the same car rated in US gallons, purely from the unit. Always check which gallon a figure refers to before comparing anything.
Significant figures
Converting an approximate measurement does not make it precise. Six feet expressed as 1.8288 metres implies a measurement accurate to a tenth of a millimetre, when the original "six feet" was almost certainly rounded to the nearest foot.
The arithmetic will happily produce as many digits as you want, and the right number of digits comes from the input, not from the calculation. Carrying them all is not more accurate; it is a claim about precision you cannot support.
Where this actually bites
Recipes crossing between systems, where volume and weight both diverge. Construction and engineering figures. Medical dosing, where the consequence of a factor-of-ten slip is not academic. And oven temperatures, where the offset trap appears in domestic life — 180 in one scale is nothing like 180 in the other.
Everything runs in your browser with no data source needed at all, which is the neat contrast with the currency converter: a metre is always a metre, so this works offline forever, while an exchange rate is a price that changes every second.
How to use the Unit Converter
Takes about a minute. No signup, no download, your data stays in your browser.
- 1Open the tool. Scroll up to the Unit Converter above — it loads instantly in your browser, no install needed.
- 2Enter your values. The fields come pre-filled with realistic defaults so you can see how it works — replace them with your own numbers.
- 3Read the result. The output updates instantly. Copy or share it — nothing is uploaded to a server, everything stays on your device.
Frequently asked questions
Common questions about the Unit Converter.
Is a 10 degree Celsius rise a 50 degree Fahrenheit rise?
No — it is 18. The offset in the Celsius to Fahrenheit conversion locates a point on the scale, and a difference between two points is not a point, so only the multiplication applies. Converting a temperature change the way you convert a temperature is the single most common error with these units.
Why is temperature different from every other conversion?
Because the two scales differ in both the size of a degree and the position of zero, so you need a multiplication and an offset. Length, mass and volume only need the multiplication. Kelvin shows the two parts are separable: it shares Celsius degree size but not its zero, so that conversion is an offset with no multiplication at all.
Which gallon does it use?
Check the unit labels, because it matters more than people expect. A US gallon and an imperial gallon are different sizes, and the difference propagates into derived units — miles per gallon is not comparable between the two systems even though the phrase is identical.
Are the conversion factors exact?
Many of them, yes. An inch is defined as exactly 25.4 millimetres and a pound as exactly 0.45359237 kilograms — these are definitions rather than measurements, so they will not be revised by better instruments. That is why converting a whole number between those units is exact rather than approximate.
How many decimal places should I keep?
As many as the input justifies, and no more. Six feet converted to 1.8288 metres claims accuracy to a tenth of a millimetre when the original was rounded to the nearest foot. The calculation will produce any number of digits; the meaningful count comes from the measurement, not the arithmetic.
What is special about minus 40?
It is the one temperature that reads the same on both Celsius and Fahrenheit — the point where the two scales cross. A useful sanity check: if a conversion of minus 40 gives you anything other than minus 40, something is wrong with the arithmetic.
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