How to use the unit converter
Start with what you're measuring, not with the unit names. Length converts to length and volume to volume. You can't turn meters into square meters, because that needs a second dimension.
Every option shows its full name and system. Gallons, pints, megabytes and kilobytes all come in more than one size, so the labels tell you which one you're picking.
- Choose the measurement type: length, mass, temperature, area, volume, speed, time or digital data.
- Enter the value. Negative numbers, decimals and scientific notation all work.
- Pick the unit you have and the unit you want. Swap units flips the direction without retyping.
- Set the displayed precision from 4 to 12 significant digits. The stored factors don't change.
- Press Convert units and read the result, the factor, the base-unit value, the reverse check and the full table.
Metric conversion examples
Each row below uses the same exact factors the converter stores. The last column says why the unit label changes the answer.
| You have | You want | Result | Why the label matters |
|---|---|---|---|
| 10 m | Feet | 32.80839895 ft | The international foot is exactly 0.3048 m |
| 100 lb | Kilograms | 45.359237 kg | Avoirdupois pound, not troy |
| 60 mph | km/h | 96.56064 km/h | A mile is exactly 1,609.344 m |
| 1 U.S. liquid gal | Liters | 3.785411784 L | Not the Imperial gallon |
| 1 Imperial gal | Liters | 4.54609 L | About 20% larger than a U.S. gallon |
| 32 deg F | Celsius | 0 deg C | Temperature needs an offset |
| 1 MB | Mebibytes | 0.9536743164 MiB | Decimal MB isn't binary MiB |
| 1 kn | km/h | 1.852 km/h | A knot is one nautical mile per hour |
The conversion formula
Every linear unit has one factor to a base unit: meters for length, kilograms for mass, liters for volume, bytes for data. The converter multiplies your value by the source factor, then divides by the target factor. That's why one factor table covers every pair.
Take 60 mph to km/h. One mph is 0.44704 m/s, and one km/h is 1/3.6 m/s. So 60 x 0.44704 x 3.6 gives 96.56064 km/h. The reverse check runs the same path backward and should land on 60 again.
Base value = entered value x source-to-base factorConverted value = base value / target-to-base factorDirect factor = source factor / target factor
Imperial to metric: the exact definitions
Since 1959, U.S. and British length and mass units have been defined from metric ones. An inch is exactly 2.54 cm, a foot is 0.3048 m and a pound is 0.45359237 kg. So any imperial to metric answer here is exact until it's rounded for display.
The U.S. survey foot, a slightly longer foot once used in land surveying, was retired by NIST at the start of 2023. This tool uses the international foot only.
- 1 inch = 2.54 cm
- 1 foot = 0.3048 m
- 1 mile = 1.609344 km
- 1 pound = 0.45359237 kg
- 1 acre = 43,560 square feet, or 0.40468564224 hectares
Celsius to Fahrenheit needs an offset
Zero degrees Celsius and zero degrees Fahrenheit are different temperatures, so a single factor can't do the job. The converter turns the reading into kelvin first, then into the scale you asked for. Body temperature of 37 deg C comes out as 98.6 deg F.
Anything below absolute zero (0 K, or -273.15 deg C, or -459.67 deg F) is rejected. A temperature change is a different sum: a rise of 1 deg C equals a rise of 1.8 deg F, with no offset.
K = C + 273.15K = (F + 459.67) x 5 / 9F = K x 9 / 5 - 459.67Rankine = K x 9 / 5
U.S. and Imperial gallons, MB and MiB
A U.S. liquid gallon is 3.785411784 liters. An Imperial gallon is 4.54609 liters. The pints differ too, so a British recipe or fuel figure read as U.S. units will be off by about a fifth. Pick the system the source names.
Data has the same trap. A decimal megabyte (MB) is 1,000,000 bytes, and a binary mebibyte (MiB) is 1,048,576 bytes. Older software often writes MB when it means MiB, which is why a drive can look smaller on your computer than on the box. Bits and bytes differ by a factor of eight.
How many digits to keep
The factors are exact, but your measurement usually isn't. A board recorded as 36 feet doesn't become accurate to the micrometer just because the metric answer has eight decimals. NIST advises rounding the result to match the precision of the original number.
Use more digits during working steps, then report what the source justifies. For lab, trade, medical or safety work, follow the standard that governs it.
Sources
These references back the unit definitions, prefixes and rounding advice on this page.