Unit Converter

Eight categories, each anchored to one base unit

Every conversion here works the same way. Your figure is multiplied by the factor that expresses its unit in a base unit, then divided by the factor for the unit you want. Length uses the metre, Weight/Mass uses the kilogram, Volume uses the litre, Area uses the square metre, Speed uses metres per second, Time uses the second and Data Storage uses the byte. The factors are the internationally agreed exact ones, not rounded shortcuts: a mile is 1609.344 metres, a pound is 0.45359237 kilograms, an inch is 0.0254 metres, an acre is 4046.8564224 square metres and a knot is 0.5144444 metres per second.

Temperature is the exception, because Celsius, Fahrenheit and Kelvin do not share a zero point, so a single multiplier cannot work. Your value is converted into Celsius first, then out again: Fahrenheit in becomes (F minus 32) times 5/9, Kelvin in becomes K minus 273.15, and the reverse formulas are applied on the way out.

The units you can pick in each tab

• Length: kilometre, metre, centimetre, millimetre, mile, yard, foot, inch and nautical mile.
• Weight / Mass: tonne, kilogram, gram, milligram, pound, ounce and stone.
• Temperature: Celsius, Fahrenheit and Kelvin.
• Volume: cubic metre, litre, millilitre, US gallon, quart, pint, cup, fluid ounce, tablespoon, teaspoon and imperial gallon.
• Area: square kilometre, hectare, square metre, square centimetre, square mile, acre, square yard, square foot and square inch.
• Speed: metres per second, kilometres per hour, miles per hour, feet per second and knots.
• Time: second, minute, hour, day, week, average month and average year.
• Data Storage: bit, byte, then KB, MB, GB and TB in powers of 1000 alongside KiB, MiB, GiB and TiB in powers of 1024.

Worked example

Open the Area tab, set the left unit to Acre, type 5, and set the right unit to Hectare. Internally 5 is multiplied by 4046.8564224 to give 20234.282112 square metres, then divided by 10000, and the display reads 5 Acre (ac) = 2.0234282 Hectare (ha). Press the swap arrow and the same figures run the other way. Below the result, a small reference table shows the everyday equivalents for that category, such as 1 hectare equals 2.47105 acres.

How results are rounded

Answers are shown to eight significant figures and then trimmed of trailing zeroes, so 2.0234282 rather than 2.02342821120000. Numbers smaller than 0.0001 or larger than 1e15 switch to exponential notation with six decimal places, which keeps a byte count in terabytes or a millimetre value in miles readable. If the input box is empty or not a number, the result shows a dash instead of guessing.

Everyday situations this covers

Cooking from a US recipe while standing in an Australian kitchen is the classic one, since cups, sticks and fluid ounces need turning into millilitres and grams. Beyond that: reading a real estate listing that quotes a block in square metres when you think in acres, converting your own weight into stone for a UK form, checking whether a 55 pound airline baggage limit clears your 26 kilogram suitcase, working out what 65 mph means on a speed sign, converting a maritime chart from knots, sizing a video export when a platform states a 500 MB cap and your file manager reports MiB, or working out how many seconds are in a billing period.

Two notes the tool shows on screen. Volume defaults to US customary measures, so imperial pints and gallons are larger and the imperial gallon is listed separately at 4.54609 litres. Time uses an average month of 30.44 days and an average year of 365.25 days, which is fine for estimates but not for calendar arithmetic.

What it will not do

This is a single value converter, not a calculator. It will not parse "5 ft 9 in" as one entry, handle currency, convert fuel economy between litres per 100 km and miles per gallon, or do unit algebra across categories. It also will not convert between calendar dates. Nothing you type is transmitted, and there is no limit on how many conversions you run.

Better fits elsewhere

• Counting days between two calendar dates belongs in Date Difference Calculator.
• Epoch values and ISO timestamps are handled by the Unix Timestamp Converter.
• Height and weight together feed the BMI Calculator.
• Working out increases or discounts is the job of the Percentage Calculator.
• Measuring a block of land from a map is covered by Land Quote Calculator and the guide on measuring land area from satellite maps.

FAQ

How exact are the conversion factors?

They are the defined values, not approximations. An inch is exactly 2.54 centimetres and a pound is exactly 0.45359237 kilograms, so the only rounding happens when the answer is displayed to eight significant figures.

Why does my hard drive show less space than the box claimed?

Manufacturers count a gigabyte as 1,000,000,000 bytes while many operating systems display gibibytes, which are 1,073,741,824 bytes. Switch between the two in the Data Storage tab to see the difference for your own figure.

Are the volume units US or imperial?

The gallon, quart, pint, cup, fluid ounce, tablespoon and teaspoon are US customary. The imperial gallon is listed as its own option at 4.54609 litres, and imperial pints are larger than US pints.

Why is a month listed as an average?

Months vary between 28 and 31 days, so the Time tab uses 30.44 days for a month and 365.25 days for a year. Use a date calculator when you need exact calendar arithmetic.

Does anything get uploaded?

No. Every calculation runs in plain JavaScript on your device, so no value you type leaves the page.