Unit Converter

How the converter works

Pick a category, choose your from and to units, and type a number. The result updates as you type, calculated on your device with the exact conversion factors defined by international standards — 1 inch is exactly 25.4 millimeters, 1 pound is exactly 0.45359237 kilograms. Nothing you enter leaves your browser.

Why converters disagree sometimes

If two conversion sites give you slightly different answers, one of them is rounding early. Cheap converters store factors with a few decimal places and compound the error when chaining conversions. We convert through the base unit with full-precision factors and round only the displayed result.

The other classic source of confusion is ambiguous units. A US gallon is not an imperial gallon. A gigabyte is not a gibibyte, even though your operating system may mix them up. Where a unit has variants, we label the one we use.

The categories that matter most

Length and weight cover most everyday needs — recipes, shipping, travel. Temperature handles the Celsius-Fahrenheit divide. Data sizes settle the classic argument about why a 1 TB drive shows up as 931 GB. Volume covers cooking across metric and US kitchens, and speed translates between km/h, mph, and knots.

Guides from Unit Converter

Longer explainers written for this site. Each one carries a review date.

• Why the world has two measurement systems · 5 min read
  Three countries still hold out against metric. The history is stranger than you think, and the practical advice is simpler than the debate.
• Why your 1 TB drive shows only 931 GB · 4 min read
  Nobody stole your storage. Drive makers and Windows are counting with different definitions of the same word, and both are technically right.
• Fahrenheit, Celsius, Kelvin: why three scales exist · 5 min read
  One scale was built on brine, one on water, one on physics itself. Where each came from and the honest case for each.
• Cups, grams, and why recipes fail across the Atlantic · 5 min read
  A cup of flour can vary by 30% depending on who scooped it. The unit traps hiding in international recipes, and how to bake around them.
• The most expensive unit-conversion mistakes in history · 5 min read
  A $327 million spacecraft, a jet gliding without fuel, and a 143-year-old bridge — what happens when nobody double-checks the units.
• The mental shortcuts for converting units without a calculator · 5 min read
  You don’t need to memorize tables. A handful of anchor numbers and rough tricks get you within a few percent for almost anything.

See all guides →