Everything you need for conversions

Which converter do you need?

Each converter covers a whole family of units in both directions, so there is one page per quantity rather than one page per pair — kilograms to pounds and pounds to kilograms are the same page.

Distance, height and dimensions

Length handles millimeters through miles, which covers most measuring, shipping and DIY questions. Height is separate because a person’s height is written as feet and inches together rather than as a single decimal, and that formatting is the whole difficulty.

Weight and mass

Weight spans milligrams to stone, including the ounce and pound conversions that recipes, parcel limits and gym plates all need.

Temperature

Temperature is the one conversion that is not a simple multiplication: Celsius and Fahrenheit have different zero points as well as different step sizes, so the page states the formula rather than only the answer.

Area and volume

Area covers square meters, square feet, acres and hectares for land and flooring. Volume covers liters, milliliters, gallons, quarts and cups — where the US and Imperial gallon differ, and the page says which one it used.

Speed

Speed converts between mph, km/h, m/s and knots, which is the set that covers driving, running and weather reports.

File and storage sizes

Data storage converts bytes through terabytes. It is worth reading the page rather than only the number, because the reason a "1 TB" drive shows as less in the operating system is a unit disagreement, not a missing part of the disk.

What to know before trusting a converted number

A unit converter looks like the simplest thing on a website and quietly is not. These are the places the answer can be right and still not be what you needed.

• Rounding is display, not arithmetic. The conversion runs at full precision and the result is rounded for reading. Chaining several rounded figures by hand will drift; convert once from the original value instead.
• US and Imperial units share names and not sizes. Gallons, pints, fluid ounces and tons all differ between the two systems. These pages use US customary units, because that is who the site is written for, and each page says so.
• Mass is not weight, and volume is not mass. Converting cups of flour to grams needs the density of flour, which is not a unit conversion and is not what these tools do.
• Storage units are ambiguous by convention. Drive manufacturers count a terabyte as 1,000,000,000,000 bytes; many operating systems display it in units of 1,024. Both are defensible and they do not agree.
• A converter is not a measurement. It is exactly as accurate as the figure you type into it, and no more.

Every conversion runs in your browser, so the numbers you enter go nowhere — the account of that is on Security and File Processing.