Unit Converter

Fast, accurate unit conversion

Convert once, read everything

Pick a category tab, type a value, choose its unit — and the full results grid updates at once. Instead of converting miles to kilometers, then checking feet, then yards in three separate steps, one input shows the value in every unit of the category simultaneously. That layout turns the converter into a comparison table: type 1 with any unit selected and you effectively get the category's entire conversion chart, which is often the real question behind a conversion ("how big is a hectare, roughly?").

The conversions that trip people up

Two categories deserve a note. Temperature is not a simple multiplication: Celsius, Fahrenheit and Kelvin are offset scales, so 0 °C is 32 °F and the formulas involve addition as well as scaling — the converter applies the exact formulas rather than a factor. Data size carries a naming trap: storage marketing counts a megabyte as 1,000,000 bytes (decimal), while operating systems often report the binary 1,048,576-byte unit, which is properly called a mebibyte. That mismatch alone explains why a "500 GB" drive shows up smaller in your file manager — check both readings here when the numbers matter.

Where a converter earns its keep

Typical daily uses: translating a recipe between grams and ounces, sanity-checking a shipping weight quoted in pounds, converting a running pace between km/h and mph, estimating whether a video file fits on a drive, or reading an American spec sheet in metric. Because the math runs locally, the page also works mid-flight or anywhere offline once it has loaded — type, read, done.

Step-by-step: getting an answer in three actions

Click the category tab — Length, Mass, Temperature, Data, Speed, Time, Area or Volume — type the number into the value field, and choose the unit it is currently in from the dropdown beside it. That is the whole workflow; the results grid below refreshes on every keystroke. Each cell shows the unit name, its symbol and the converted value, so a pace of 12 km/h is read off as 7.456 mph, 3.333 m/s, 6.479 knots and 10.94 ft/s at once. Two details are easy to miss. The dropdown lists every unit in the category, so it doubles as a quick reference for which units exist (Stones and Nautical miles are there alongside the obvious ones). And the value field accepts decimals, negatives and scientific notation such as 2.5e9, which matters in the Data category where byte counts get large. Values are formatted to eight significant digits and very large or very small results switch to exponential form, so a conversion never silently rounds to zero.

How the conversions work under the hood

Seven of the eight categories use a base-unit table: every unit is stored as the value of one of it in the category's SI base — metres for length, kilograms for mass, bytes for data, seconds for time, square metres, litres and metres per second. Converting is two multiplications: the input times its unit's factor gives the base quantity, and dividing by each target factor gives every cell in the grid. The factors are the exact definitions where one exists — an international inch is 0.0254 m, a pound is 0.45359237 kg, a US gallon is 3.785411784 L, a knot is one nautical mile (1852 m) per hour — so round-trips come back to the value you typed. Temperature is the exception because its scales have different zero points; the converter first moves the input to Celsius ((F − 32) × 5/9, or K − 273.15) and then out to the target, which is why −40 lands on −40 in both Celsius and Fahrenheit and why 0 K reads as −273.15 °C. Data uses two parallel ladders in one table: decimal KB/MB/GB/TB stepping by 1000 and binary KiB/MiB/GiB stepping by 1024, with bits at one-eighth of a byte, so the grid shows both readings of the same quantity side by side.

Common mistakes and how to avoid them

Imperial versus US customary volume. The Volume category uses US gallons, pints and cups. A UK (imperial) pint is 568 mL rather than 473 mL and an imperial gallon is about 20 % larger — convert British recipes to millilitres by hand before trusting a cup count. Megabytes in network speeds. Broadband is sold in megabits per second; file sizes are in megabytes. Enter the Mb value in the Data category as Bits × 10⁶ (or divide by 8) before comparing with a download size, otherwise the estimate is eight times too optimistic. Weight and mass. The Mass category converts pounds, ounces and kilograms as mass, which is what scales and shipping labels mean; it is not a force conversion. Years and months. A year here is the Julian 365.25 days (31,557,600 s) — fine for durations, wrong for calendar arithmetic; months are deliberately absent because they have no fixed length. Reading precision into the display. Eight significant digits does not mean the source measurement had eight; a 1.5 kg package is 3.3069339 lb in the grid but "3.3 lb" on the label.

Further reading

Working with units inside spreadsheets and exports? CSV, JSON and XLSX conversion pitfalls covers locale decimals and number formatting; for data-size questions about images, WebP vs AVIF vs PNG vs JPG compares real file sizes. Browse all guides.

Frequently asked questions