Measurement Tool
Unit Converter
Convert between more than a hundred units across fifteen categories — length, weight, temperature, volume, digital storage, energy and more. Exact conversion factors, every unit shown at once, and a link you can share.
- 15 categories
- 100+ units
- Exact factors
- All units at once
- Shareable links
- Free
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📏 LengthThat is not a number the converter can read.
Common conversions
Your value in every unit
| Unit | Value | Actions |
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Display & history
Conversions are always calculated at full precision — these settings only change how the result is displayed. Turn grouping off when you need a plain number for a spreadsheet.
Recent conversions
Quick reference table
| km | mi |
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Updates with the two units you have selected. Handy to print or screenshot.
Every conversion runs in your browser. Nothing you type is uploaded, and your history stays in local storage on this device.
What This Unit Converter Does
A unit converter turns a measurement in one unit into the same measurement in another. This one covers fifteen categories and more than a hundred units, and it is built around three things most converters skip:
- Exact factors, not rounded ones. An inch is exactly 0.0254 m and a pound is exactly 0.45359237 kg by international agreement. Those definitions are used verbatim, so errors do not accumulate.
- Scales that are not simple ratios. Temperature has an offset and fuel economy is inverted. Multiplying by a single factor gives the wrong answer for both, so each is handled with its real formula.
- Units that share a name. A ton, a gallon, a calorie and a horsepower all mean different things in different places. Each variant is listed separately with a note, so you are never guessing which one you got.
The all-units table shows your value in every unit of a category at once, which usually answers the follow-up question before you ask it.
Categories and What They Cover
Nanometre to light year, including inch, foot, yard, mile, nautical mile and furlong.
Milligram to metric ton, plus ounce, pound, stone, carat, grain and both US and UK tons.
Celsius, Fahrenheit, Kelvin, Rankine and Réaumur — all with proper offset handling.
Millilitre to cubic metre, with separate US and imperial gallons, pints, cups and fluid ounces.
Square millimetre to square mile, plus acre, hectare and are.
m/s, km/h, mph, ft/s, knots, Mach and the speed of light.
Nanosecond to decade. Month and year use a mean Gregorian year and say so.
Bits and bytes with decimal (kB, MB, GB) and binary (KiB, MiB, GiB) kept separate.
bit/s through Gbit/s and B/s through MB/s — the megabit versus megabyte confusion, solved.
Pascal, bar, psi, atmosphere, torr and mmHg, plus the hPa used in weather reports.
Joule, calorie, food calorie, watt hour, kWh, BTU, electronvolt and foot-pound.
Watt, kilowatt, both mechanical and metric horsepower, and BTU per hour.
Degree, radian, gradian, turn, arcminute and arcsecond.
Hertz through gigahertz, plus revolutions per minute.
L/100km, km/L and both US and UK mpg — converted with the correct inversion.
Four Conversions People Get Wrong
Temperature is not a ratio. Celsius and Fahrenheit have different zero points, so you cannot scale between them. The formula is °F = °C × 9/5 + 32. A quick sanity check: −40 °C and −40 °F are the same temperature, and any converter that disagrees is broken.
Fuel economy runs backwards. Miles per gallon measures distance per fuel; litres per 100 km measures fuel per distance. A higher mpg means a lower L/100km, so the conversion is a division: L/100km = 235.21 ÷ mpg. And US and UK mpg differ by about 20% because they use different gallons.
Your hard drive is not lying to you. Manufacturers count a terabyte as a trillion bytes; most operating systems count in units of 1,024. One trillion bytes is 931.32 GiB, so a "1 TB" drive genuinely holds what it says — the two systems just count differently. Decimal and binary units are listed separately here.
Megabits are not megabytes. Internet plans are sold in megabits per second, download managers report megabytes per second, and there are eight bits in a byte. A 100 Mbps line tops out around 12.5 MB/s.
Common Conversion Factors
| Conversion | Multiply by | Exact? |
|---|---|---|
| km → miles | 0.621371 | derived from an exact definition |
| miles → km | 1.609344 | exact |
| cm → inches | 0.393701 | derived from an exact definition |
| inches → cm | 2.54 | exact |
| kg → pounds | 2.204623 | derived from an exact definition |
| pounds → kg | 0.45359237 | exact |
| litres → US gallons | 0.264172 | derived from an exact definition |
| US gallons → litres | 3.785411784 | exact |
| m² → ft² | 10.763910 | derived from an exact definition |
| km/h → mph | 0.621371 | derived from an exact definition |
| hp → kW | 0.745700 | mechanical horsepower |
| kWh → MJ | 3.6 | exact |
The figures above are rounded for reading. The converter itself uses the full exact values, so a round trip returns the number you started with.
Where People Use It
US cups and imperial pints are different sizes. Convert to grams or millilitres and the recipe works.
km/h to mph, litres to gallons, and °C to °F for the forecast.
Pressure, power and torque units across metric and imperial documentation.
Kilograms to pounds and stone, plus food calories to kilojoules.
Storage in decimal versus binary, and bandwidth in megabits versus megabytes.
Energy in joules, calories and electronvolts, angles in degrees and radians.
Square feet, square metres, acres and hectares for listings and plans.
Metric and mechanical horsepower differ, and so do US and UK mpg.
Frequently Asked Questions
What is a unit converter?
A unit converter changes a measurement from one unit into another — kilometres into miles, kilograms into pounds, Celsius into Fahrenheit. This one covers fifteen categories and more than a hundred units, and shows the value in every unit of a category at once.
How do I convert km to miles?
Multiply kilometres by 0.621371. One mile is exactly 1,609.344 metres by international definition, so 100 km is 62.14 miles. Pick Length, set the units to kilometre and mile, and the tool does it as you type.
How do I convert kg to lbs?
Multiply kilograms by 2.20462. One pound is exactly 0.45359237 kilograms, which is an exact definition rather than a rounded figure, so 70 kg is 154.32 lb.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32, so 20 °C is 68 °F. Temperature is not a simple ratio because the scales have different zero points, which is why a converter that only multiplies gets it wrong. A useful check: −40 °C and −40 °F are the same temperature.
Why is a US gallon different from a UK gallon?
They are simply different units that share a name. A US gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres, so the UK gallon is about 20 percent larger. Both are listed separately here so you never have to guess which one is meant.
What is the difference between a US ton and a UK ton?
A US short ton is 2,000 pounds and a UK long ton is 2,240 pounds, while a metric ton is 1,000 kilograms. All three are listed separately, because picking the wrong one is a 10 percent error.
Why does my 1 TB hard drive show as 931 GB?
Because two different definitions are in use. Drive makers sell a terabyte as one trillion bytes, while operating systems usually count in binary units of 1,024. One trillion bytes is 931.32 gibibytes, so nothing is missing — the two systems are just counting differently. This tool lists decimal and binary units separately so you can see both.
How do I convert Mbps to MB/s?
Divide by eight, because there are eight bits in a byte. A 100 Mbps connection downloads at about 12.5 MB/s at best. Internet plans are advertised in megabits while download managers usually report megabytes, which is why the numbers look so different.
How do I convert mpg to L/100km?
Divide 235.21 by the US mpg figure, so 30 mpg is about 7.84 L/100km. Fuel economy is inverse: a higher mpg means a lower L/100km, so you cannot convert it by multiplying. The tool handles that inversion for you.
Is a US mpg the same as a UK mpg?
No. They use different gallons, so the same car scores about 20 percent higher in UK mpg than in US mpg. Both are listed separately in the fuel economy category.
How accurate are these conversions?
Every factor is either an exact international definition — the inch, foot, mile, pound, gallon, atmosphere and nautical mile all have one — or is marked with a note explaining the assumption. Results are computed at full double precision and only rounded for display, and you control how much.
Can I see a value in every unit at once?
Yes. The all-units table below the converter shows your number in every unit of the current category simultaneously, with a copy button on each row. It is usually quicker than running a second conversion.
Can I share or bookmark a conversion?
Yes. The web address updates as you work, so bookmarking the page keeps the exact conversion. The Share button copies that link to your clipboard.
Can I control the number of decimal places?
Yes. Choose automatic, a fixed number of decimal places, or scientific notation, and set the precision from zero to twelve. You can also turn off digit grouping when you need a plain number to paste into a spreadsheet.
What units does the converter support?
Length, weight and mass, temperature, volume, area, speed, time, digital storage, data transfer, pressure, energy, power, angle, frequency and fuel economy — fifteen categories in total, with more than a hundred individual units.
Does it work offline?
Once the page has loaded, yes. Every conversion is calculated in your browser with no network request, so the tool keeps working if your connection drops.
Is my data sent anywhere?
No. Nothing you type is uploaded. Your recent conversions and display preferences are stored in your own browser only, and you can clear them at any time.
Is this unit converter free?
Yes. It is free, needs no account, and has no limits or watermarks.