Unit & Measurement Converter
Convert between length, mass, volume, temperature, area, speed, pressure, energy, power, data storage, time and fuel economy.
How this is calculated
Most categories convert through a base unit — your value is multiplied by a fixed factor to reach the base unit (e.g. metres, kilograms, litres), then divided by the target unit's factor. Temperature and fuel economy aren't linear, so they use their own formulas instead: temperature converts through Celsius, and fuel economy inverts through litres per 100 km since "more" doesn't mean the same thing across L/100km and mpg.
Data storage units are a special case worth knowing about: KB/MB/GB use decimal (SI) prefixes where each step is ×1000, while KiB/MiB/GiB use binary prefixes where each step is ×1024 — both are included here because operating systems, storage manufacturers, and network speeds don't consistently use the same convention, which is why a "1 TB" drive often shows up as roughly 0.909 TiB once formatted.
Frequently asked questions
- How accurate are these conversions?
- Conversions use standard internationally recognised conversion factors (SI, NIST, and imperial/US customary definitions), shown to up to 10 significant figures. Temperature and fuel economy use their exact non-linear formulas rather than a simple multiplier.
- Why do data storage units have two sets of prefixes?
- KB/MB/GB use decimal (SI) prefixes — 1000 per step, the convention storage manufacturers and network speeds use. KiB/MiB/GiB are the unambiguous binary prefixes defined by IEC 80000-13 — 1024 per step, matching how operating systems typically report file and drive sizes internally. Both are included here since real-world usage mixes the two, e.g. a "1 TB" drive shows up as roughly 0.909 TiB in your OS.
- What US/UK volume differences should I know about?
- US customary and UK imperial units share names (gallon, pint, fluid ounce) but differ in size — a US gallon is about 3.785 litres, while a UK (imperial) gallon is about 4.546 litres. Pick the right variant from the unit list for your region.
- What unit systems are supported?
- The metric (SI) system, US customary units, and UK imperial units — including cases where US and UK units share a name but differ in size (like gallons), which are listed as separate options rather than merged into one.
- How is the conversion calculated?
- Most categories convert through a shared base unit — your value is multiplied by a fixed factor to reach that base unit, then divided by the target unit's factor. Temperature and fuel economy don't follow this pattern since they aren't simple linear scales, so they use dedicated formulas instead.
- What is the difference between imperial and US customary units?
- Both systems share unit names inherited from the same historical British system, but many have different sizes today — a UK (imperial) gallon is roughly 20% larger than a US gallon, for example. The two systems diverged when the US and UK standardised their measurements independently.
- Which unit categories are covered?
- Length, mass, volume, temperature, area, speed, pressure, energy, power, data storage, time, and fuel economy — twelve categories in total, each with the common units used in that domain.
- Can I convert between metric and imperial?
- Yes — every category lets you pick any unit as the "from" and any other as the "to," including mixing metric and imperial units freely (e.g. metres to feet, or kilograms to pounds).
Use this in your own app
Every calculator on Stupidly Clever has a matching REST API and MCP tool that runs the same underlying logic — including this one, via GET /v1/unit-converter.
curl "https://api.stupidlyclever.com/v1/unit-converter?category=length&from=m&to=ft&value=1" -H "Authorization: Bearer YOUR_KEY"