Unit Converter — length, weight & temperature online

Convert between metric and imperial units for length, mass, temperature, area, volume and speed. Free, instant, and works offline in your browser.

About the Unit converter tool

Two systems of measurement are in daily use and neither is going away. Recipes come in cups and ounces or in grams and millilitres depending on where they were written. Technical specifications mix millimetres and inches within the same document. Travel means reading distances and temperatures in whatever the destination uses. Converting between them is constant background work for anyone who reads, buys or builds across borders.

Most conversions are a single multiplication, which is why a table of factors would do — but remembering that a mile is 1.609 kilometres and a pound is 0.4536 kilograms, and getting the arithmetic right under time pressure, is exactly where errors creep in. Temperature is the genuine exception: Celsius and Fahrenheit have different zero points as well as different scales, so it needs an offset and a ratio rather than a single factor, and it cannot be done by rounding in your head.

The unit that causes the most trouble is the one that looks simplest. Data sizes have two competing definitions — a kilobyte is 1,000 bytes to a storage manufacturer and 1,024 bytes to an operating system — which is why a drive sold as 1 TB shows up as roughly 931 GB once connected. Nothing is missing and nothing is faulty; the two parties are using different definitions of the same word.

Fluid measures hide a similar trap. A US fluid ounce and an imperial fluid ounce differ by about four percent, and a US pint is 16 fluid ounces where an imperial pint is 20 — so an American recipe and a British one calling for a pint want noticeably different amounts. For cooking the discrepancy is usually survivable; for anything where proportion matters, it is worth being explicit about which system a figure came from.

How it works

Pick a category

Length, weight, temperature, area, volume, speed or data. Each offers the units that belong to it.

Choose your units

Set what you are converting from and to. The relevant metric and imperial options are both available.

Read the result

The answer updates as you type. Everything is calculated locally, so it works with no connection at all.

Frequently asked questions

Why does my 1 TB drive show as 931 GB?: Because two definitions of the same prefix are in use. Storage manufacturers count a terabyte as a trillion bytes; operating systems traditionally count it as 1,024 raised to the fourth power, which is about 10 percent more bytes per unit. Nothing is lost — the drive holds what was advertised, and the two parties are simply measuring with different rulers.
How do I convert Celsius to Fahrenheit in my head?: Double the Celsius figure and add 30 for a rough answer that is close enough for weather — 20°C becomes about 70°F, which is only two degrees out. The exact formula multiplies by 1.8 and adds 32. The approximation drifts at extremes, so use the real calculation for anything involving cooking, medicine or equipment tolerances.
Are US and imperial units the same thing?: For length and weight essentially yes, but for volume no. A US fluid ounce is about four percent larger than an imperial one, and a US pint holds 16 fluid ounces against the imperial 20 — so an imperial pint is roughly 20 percent bigger. Gallons differ substantially too, which matters when comparing fuel economy figures between countries.
How accurate are the conversions?: They use the standard internationally defined factors, so results are exact to the precision displayed. Most conversions between metric and imperial are defined exactly by agreement — an inch is precisely 25.4 millimetres — so the only rounding is in how many decimal places are shown, not in the underlying arithmetic.
Why is weight in kilograms rather than mass?: Strictly, kilograms measure mass and weight is a force, so the everyday usage is technically loose. In ordinary life on Earth the distinction makes no practical difference, and every scale, recipe and shipping form uses the words interchangeably. The conversions here follow common usage rather than physics terminology.
Can I convert cooking measurements like cups?: Volume conversions cover cups, millilitres, litres and fluid ounces. The caution is that dry ingredients measured by volume are unreliable — a cup of flour can vary by a third depending on how it was packed. When a recipe gives weights, use them; they are the reason baking instructions in grams produce more consistent results.
Does it work offline?: Yes. Every conversion is arithmetic performed in your browser tab with no network involved, so once the page has loaded it continues to work with the connection off — which is exactly when you tend to need it, standing in a foreign shop or kitchen without reliable data.