Type a number, pick where it's coming from, and see it converted into every other unit in that category at once — no dropdown-hunting. Built for people who convert units more than once a week: engineers checking a spec, cooks scaling a US recipe, students doing physics homework at 11pm.
Every measurement is a number tied to a scale. Converting between units means re-expressing the same real-world quantity — a length, a mass, a temperature — on a different scale. That's straightforward when both scales share a fixed ratio (a mile is always 1.609344 kilometers), and it gets trickier when the scales don't start at the same zero point, which is exactly what happens with temperature.
Length conversions are the ones people search for most, mostly because the US (plus Liberia and Myanmar) sticks with imperial units while nearly everywhere else uses metric. Recipes, road signs, and height all run into this.
Kilograms and pounds get used interchangeably in everyday speech, even though mass and weight aren't technically the same thing. For daily use, here's what matters:
This is the one category where you can't just multiply. Celsius, Fahrenheit, and Kelvin don't share a zero point, so converting needs an offset as well as a ratio.
This is the conversion that genuinely confuses people, and it's not their fault — the industry uses two different definitions of the same prefixes. Storage makers (and the SI system) define a kilobyte as 1,000 bytes. Operating systems have historically shown a kilobyte as 1,024 bytes, because computers count in binary and 1,024 (2¹⁰) is a round number there. That's why a drive sold as “1 TB” shows up as roughly 931 GB in Windows. To avoid the confusion, this tool includes both: KB/MB/GB/TB for the decimal definition and KiB/MiB/GiB/TiB for the binary one.
Recipe conversions are their own headache because “a cup” isn't the same size everywhere, and tablespoons/teaspoons are easy to mix up mid-recipe. The values here use US customary measurements, which is what most recipe sites default to.
The tool above covers all of these plus Speed, Pressure, Energy, Power, and Angle — eleven categories in total, with more added when there's a good reason to.
Exactly 1.609344 kilometers. It's been the internationally agreed definition since 1959, when English-speaking countries standardized the mile at exactly 5,280 feet.
Mostly history. Fahrenheit was standard across the British Empire until the mid-20th century; almost everywhere else switched to Celsius as part of a broader move to the metric system, but everyday measurement in the US was never fully converted.
No — a UK (imperial) gallon is 4.546 liters, about 20% bigger than a US gallon at 3.785 liters. Recipes and fuel-economy figures from the UK need converting separately if you're used to US gallons.
A gigabyte (GB) is 1,000,000,000 bytes under the decimal definition most manufacturers use. A gibibyte (GiB) is 1,073,741,824 bytes, the binary definition your operating system often uses instead. They're close but not identical — which is why storage devices seem to “lose” capacity once formatted.
Because Celsius and Fahrenheit don't start at the same zero. Length and mass conversions are pure ratios — multiply by a constant — but temperature scales are also offset from each other, so the formula needs both a multiplication and an addition step.
Where a conversion factor is defined exactly — inches to centimeters, or Celsius to Kelvin — yes. Where it isn't, like US cup sizes that vary slightly by source, we use the most widely accepted value and note it in the guide above.