Unit Converter
Convert 15 kinds of measurement between metric, imperial and US units, with feet and inches, stone and pounds, and fuel economy.
For tape measures and woodwork: shows inches to the nearest 1/16 and so on.
How your conversion is worked out
Every unit is turned into one base unit first, then into the unit you want.
- 1
Pick the units
100 cm →
inches - 2
Into metres
100 × 0.01 =
1 m - 3
Out to inches
1 ÷ 0.0254 =
39.37008 in - 4
The shortcut
1 cm =
0.393701 in
Read more: conversion factors, temperature, fuel economy, data and land units
| From | To | Multiply by |
|---|---|---|
| Inches | Centimetres | 2.54 (exact) |
| Feet | Metres | 0.3048 (exact) |
| Miles | Kilometres | 1.609344 (exact) |
| Pounds | Kilograms | 0.45359237 (exact) |
| US gallons | Litres | 3.785411784 |
| Acres | Square metres | 4,046.86 |
| Knots | Kilometres per hour | 1.852 (exact) |
| Pounds per square inch | Kilopascals | 6.894757 |
| Horsepower | Kilowatts | 0.7456999 |
| Kilocalories | Kilojoules | 4.184 (exact) |
The formula
value in base unit = value × factor of the unit you have
new value = value in base unit ÷ factor of the unit you want
(temperature and fuel economy use the formulas below)
Worked example
100 centimetres in inches: first into metres, 100 × 0.01 = 1 m. Then out to inches, 1 ÷ 0.0254 = 39.37008 in. That's also 3 ft 3.37 in. As a shortcut, 1 cm = 0.393701 in.
More: a 10 km run is 10 ÷ 1.609344 = 6.21 miles. Someone 6 ft tall is 6 × 0.3048 = 1.83 m. A 30 °C day is 30 × 9 ÷ 5 + 32 = 86 °F.
Temperature
°F = °C × 9 ÷ 5 + 32
°C = (°F − 32) × 5 ÷ 9
K = °C + 273.15
°R = K × 9 ÷ 5
A quick way to estimate: double the Celsius figure and add 30. 20 °C is about 70 °F (exactly 68 °F).
US or UK?
US and UK (imperial) gallons, pints and fluid ounces are different sizes. A UK gallon is about 20% bigger than a US gallon. Cups and spoons here are US measures, which most online recipes use.
Fuel economy
Litres per 100 km goes down as a car gets more efficient, while km per litre and miles per gallon go up, so they're upside down to each other:
km/L = 100 ÷ (L/100 km)
US mpg = 235.215 ÷ (L/100 km)
UK mpg = 282.481 ÷ (L/100 km)
So 8 L/100 km is 12.5 km/L, 29.4 US mpg or 35.3 UK mpg.
Data: 1000 or 1024?
Disk makers and internet speeds use powers of 1000 (1 GB = 1,000,000,000 bytes). Computers often count in powers of 1024 (1 GiB = 1,073,741,824 bytes), which is why a "1 TB" drive shows as about 931 GB in Windows. Internet speeds are in bits: divide megabits per second by 8 to get megabytes per second, so 100 Mbps downloads about 12.5 MB each second.
Indian land units
A gaj is a square yard (0.836 m²). A cent is one-hundredth of an acre (435.6 sq ft) and a guntha is 1,089 sq ft (40 guntha to an acre). Bigha, kanal and marla change from state to state, so they're not included; check your local land records office for those.
| Handy pressure and energy facts | Value |
|---|---|
| Standard air pressure at sea level | 1013.25 hPa = 1 atm = 14.696 psi = 29.92 inHg |
| Tyre pressure 32 psi | 2.21 bar = 220.6 kPa |
| 1 food Calorie (kcal) | 4.184 kJ |
| 1 unit of electricity (kWh) | 3.6 MJ = 3,412 BTU |
| 1 ton of air conditioning (TR) | 12,000 BTU/h = 3.517 kW |
Conversion factors are exact by definition where the table says so, and otherwise from NIST SP 811 and the SI Brochure (checked 9 October 2026). A month here is an average month (30.44 days) and a year is 365.2425 days.
Common questions
How many inches is 100 cm?
100 cm is 39.37 inches, or 3 ft 3.37 in. The converter first turns 100 cm into 1 metre, then divides by 0.0254, the number of metres in an inch. As a shortcut, 1 cm = 0.393701 in. A 6 ft person is 1.83 m.
How do I convert Celsius to Fahrenheit?
Multiply by 9, divide by 5 and add 32. A 30 °C day is 30 × 9 ÷ 5 + 32 = 86 °F. To go back, take away 32 and multiply by 5 ÷ 9. For a quick estimate, double the Celsius figure and add 30.
Is a UK gallon the same as a US gallon?
No. A UK (imperial) gallon is about 20% bigger than a US gallon, and UK pints and fluid ounces are different sizes too, so pick the right one in the list. Cups and spoons here are US measures, which most online recipes use.
How do I convert L/100 km to mpg?
Divide 235.215 by the L/100 km figure for US mpg, or 282.481 for UK mpg. So 8 L/100 km is 29.4 US mpg, 35.3 UK mpg or 12.5 km/L. The numbers go opposite ways, because a lower L/100 km means a more efficient car.
Why does a 1 TB drive show as 931 GB?
Drive makers count in powers of 1000, so 1 GB is 1,000,000,000 bytes. Computers often count in powers of 1024, where 1 GiB is 1,073,741,824 bytes, so a 1 TB drive shows as about 931 GB in Windows. Both kinds of size are in the data list.
How do I convert Mbps to MB per second?
Internet speeds are in bits, and there are 8 bits in a byte, so divide megabits per second by 8. A 100 Mbps connection downloads about 12.5 MB each second. The internet speed group converts between these units for you.
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