Unit Converter
Length, mass, volume, area, speed, temperature, pressure, energy, power, data, angle, time, force and fuel economy — converted exactly, with every unit in the category shown at once.
Instant answers
Works offline once loaded
Nothing you type is sent anywhere
14 categories
All units at once
Exact definitions
What are you converting?
Result
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Your value in every unit in this category
| Unit | Value | Symbol |
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Common conversions in this category
| Conversion | Factor |
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Instructions
How to use this calculator
Step by step
- Pick a category from the tiles at the top. The unit lists rebuild themselves for whichever quantity you chose.
- Type your value, then choose the units to convert from and to. The result updates as you type — there is no button to press.
- Use the swap button between the two dropdowns to reverse the conversion without retyping anything.
- Look at the table underneath: your value is shown in every unit in the category at once, which is usually faster than converting one pair at a time.
- Change the decimal places if the automatic setting gives you more or less precision than you want, and switch to scientific or engineering notation for very large or very small numbers.
- Read the note under the result for the exact factor in both directions — handy when you want to do the conversion in your head next time.
Good to know
- Most imperial-to-metric conversions are exact by definition, not approximate. An inch is exactly 25.4 mm and a pound is exactly 0.45359237 kg — these were legally defined in 1959.
- US and imperial liquid measures are not the same. A US gallon is 3.785 L and an imperial gallon is 4.546 L, a 20% difference that has caused real navigational and cooking disasters.
- Storage manufacturers use decimal gigabytes (10⁹) and operating systems usually report binary gibibytes (2³⁰). That is why a "1 TB" drive shows as 931 GB — nothing has been lost.
- Fuel economy in miles per gallon and litres per 100 km are reciprocals, so equal changes are not equally valuable. Going from 15 to 20 mpg saves more fuel over the same distance than going from 40 to 50.
- When converting temperature differences rather than temperatures, use the ratio only: a 10 °C rise is an 18 °F rise, with no 32 added.
- Weight and mass are different quantities. Kilograms measure mass; pounds-force and newtons measure weight. On Earth the distinction rarely bites, which is why almost everyone ignores it.
The maths behind it
- Linear conversion result = value × (from factor ÷ to factor) Every category except temperature and fuel economy works this way.
- Celsius to Fahrenheit °F = °C × 9/5 + 32 And back: °C = (°F − 32) × 5/9.
- Celsius to Kelvin K = °C + 273.15 A step of one kelvin equals a step of one degree Celsius.
- Fahrenheit to Kelvin K = (°F + 459.67) × 5/9 Rankine is the absolute scale with Fahrenheit-sized degrees.
- mpg to L/100 km L/100km = 235.215 ÷ mpg (US) For imperial gallons the constant is 282.481.
- Degrees to radians rad = degrees × π / 180 A full turn is 2π radians or 400 gradians.
- Binary prefixes 1 KiB = 1024 B, 1 MiB = 1024² B Decimal prefixes use powers of 1000 instead.
Why is there no single multiplier for temperature?
Because temperature scales have different zero points as well as different step sizes — the relationship is affine rather than proportional. Multiplying 20 °C by two does not give a temperature twice as hot; it gives a different number on an arbitrary scale. Only the absolute scales, kelvin and rankine, support ratios meaningfully.
US gallon or imperial gallon — which one do I want?
If you are in the United States, the US gallon (3.785 L). If you are in the UK, Canada or the Caribbean and reading an older recipe or fuel figure, the imperial gallon (4.546 L). The 20% difference is large enough to matter for anything from baking to flight planning, so both are listed separately here.
Why does my 1 TB hard drive show as 931 GB?
The manufacturer counts a terabyte as 10¹² bytes; the operating system usually divides by 2⁴⁰ and calls the result GB when it technically means GiB. Nothing is missing — the same bytes are being described with two different prefixes. Convert between TB and TiB on this page to see exactly where the number comes from.
Are these conversion factors exact?
Most of them, yes. The international yard and pound agreement of 1959 defined the inch as exactly 25.4 mm and the pound as exactly 0.45359237 kg, and the metric system defines the rest. The exceptions are physical constants and things like the average month or Mach number, which depend on conditions — those are labelled where it matters.
What is the difference between a kilogram and a kilogram-force?
A kilogram is a mass; a kilogram-force is the weight that mass has in standard Earth gravity, which is 9.80665 newtons. Kitchen scales report mass, spring scales measure force and convert. The distinction only becomes practical away from the Earth's surface — or in engineering, where confusing the two is a classic mistake.
Why do L/100 km and mpg move in opposite directions?
They measure inverse things: one is fuel per distance and the other distance per fuel. A lower L/100 km is better; a higher mpg is better. The reciprocal relationship also means mpg is a misleading scale for comparing savings — replacing a 15 mpg vehicle with a 20 mpg one saves more fuel than replacing a 40 mpg one with a 55 mpg one.
Can I convert between mass and volume — like grams to millilitres?
Not without knowing the density of the substance. For water they happen to coincide (1 mL of water is 1 g), which is where the confusion comes from, but 1 mL of honey is about 1.4 g and 1 mL of oil about 0.92 g. Cooking conversions that ignore this are the reason baking by volume is unreliable.