Exact conversion factors, not rounded rules of thumb
A lot of quick mental-math conversions — "just multiply by two" for kilograms to pounds, for instance — are close enough for a rough estimate but genuinely wrong for anything that needs to be accurate. This tool uses the internationally defined exact conversion factors for each unit, computed instantly in your browser as you type.
Using it
- Pick the category — length, weight, or temperature.
- Choose your starting unit and enter a value.
- Read the converted result instantly in the target unit.
Why "close enough" conversions drift
Most everyday units have a precisely defined relationship to each other — an inch is exactly 25.4 millimeters, a pound is exactly 0.45359237 kilograms — figures fixed by international standards bodies, not approximations. Rough mental shortcuts like "a kilogram is about two pounds" are genuinely useful for a quick gut check, but they compound into real error over larger numbers or when a result gets used in a further calculation. This tool always uses the exact defined figures, so the result is precise regardless of how large or small the input is.
A note on temperature
Temperature is a slightly different kind of conversion than length or weight — it's not a simple multiplication, since Celsius and Fahrenheit have different zero points as well as different scale sizes. Celsius to Fahrenheit involves both a multiplication and an offset (multiply by 9/5, then add 32), which is exactly what this tool handles automatically rather than leaving you to remember the formula.
A couple of conversions people get wrong
Cups, tablespoons, and other cooking measurements sound like straightforward volume conversions, but they actually vary slightly between US customary and imperial definitions — worth double-checking which system a recipe actually intends if precision matters. Similarly, "tons" is genuinely ambiguous without more context: a US short ton, a UK long ton, and a metric tonne are three different weights, close enough to cause real confusion but not identical. Picking the right starting unit, not just the right number, is often where conversion mistakes actually happen.
Pairs well with
For splitting a bill or working out a percentage change rather than a unit conversion, the site's Tip Calculator and Percentage Calculator cover that kind of everyday math.
Frequently asked questions
+Is this unit converter really free, with no sign up?
Yes. There's no account and no limit on how many conversions you can run.
+How precise are the conversions, actually?
They use the internationally defined exact conversion factors, not rounded approximations — for example, one inch is defined as exactly 25.4 millimeters, and this tool uses that exact figure rather than a rounded "about 25" shortcut some quick-reference charts use.
+Why do some online conversions give slightly different answers?
Small discrepancies usually come from a site rounding an intermediate step, or using an older, superseded definition for a unit. Most common units (meter, kilogram, and units derived from them) have internationally agreed, exact definitions, so a correct converter should match another correct converter precisely.
+Is my data sent anywhere?
No. Every conversion is computed directly in your browser — there's no server involved, so there's nothing to send.