Unit Converter
By Talcart · Last updated July 10, 2026
Unit Converter Guide
Area Conversions
Common Units
Square Meter (m²)
Square Kilometer (km²)
Square Mile (mi²)
Square Yard (yd²)
Square Foot (ft²)
Square Inch (in²)
Hectare (ha)
Acre
Length Conversions
Common Units
Meter (m)
Kilometer (km)
Centimeter (cm)
Millimeter (mm)
Mile (mi)
Yard (yd)
Foot (ft)
Inch (in)
Pressure Conversions
Common Units
Pascal (Pa)
Kilopascal (kPa)
Bar
PSI (Pounds per Square Inch)
Atmosphere (atm)
Torr
Weight Conversions
Common Units
Kilogram (kg)
Gram (g)
Milligram (mg)
Metric Ton (t)
Pound (lb)
Ounce (oz)
Stone (st)
Volume Conversions
Common Units
Cubic Meter (m³)
Liter (L)
Milliliter (mL)
Cubic Foot (ft³)
Cubic Inch (in³)
Gallon (gal)
Quart (qt)
Pint (pt)
Time Conversions
Common Units
Second (s)
Minute (min)
Hour (h)
Day (d)
Week (wk)
Month
Year (yr)
Unit Converter
A unit converter changes a measurement from one unit to another by applying an exact conversion factor — for example, 5 miles × 1.609344 = 8.04672 kilometers. This converter covers length, weight, volume, area, temperature, speed and time, switching between metric (SI), US customary and imperial units without any lookup tables or manual arithmetic.
Key facts
- The inch has been defined as exactly 25.4 mm since the International Yard and Pound Agreement of 1959.
- The metre is defined as the distance light travels in a vacuum in 1/299,792,458 of a second (since 1983).
- Since 2019 the kilogram has been defined via the Planck constant, fixed at exactly 6.62607015 × 10^-34 J·s.
- The US gallon is exactly 3.785411784 litres, while the imperial gallon is exactly 4.54609 litres — a 20.1% difference.
What is the Unit Converter?
A unit converter is a tool that re-expresses the same physical quantity in a different unit of measurement by multiplying by a fixed, internationally agreed factor. The quantity itself never changes — 1 inch and 2.54 cm are the same length. Since the 1959 International Yard and Pound Agreement, the common imperial-metric factors are exact by definition, not measured approximations, which is why converters can agree to any number of decimal places.
How does the Unit Converter work?
Every unit is stored as a multiple of its SI base unit: the metre for length, the kilogram for mass, the litre (0.001 m³) for volume, and the second for time. To convert, the input is first multiplied into the base unit, then divided by the target unit's factor — miles to feet goes through metres (1 mile = 1,609.344 m, 1 foot = 0.3048 m). Temperature is the exception: it needs an offset as well as a scale, so °F = °C × 9/5 + 32 rather than a single multiplier.
What is the Unit Converter formula?
- Temperature uses C = (F − 32) × 5/9 etc.
Most-searched conversion factors
| From | To | Multiply by |
|---|---|---|
| 1 mile | kilometers | 1.609344 (exact) |
| 1 kilometer | miles | 0.621371 |
| 1 inch | centimeters | 2.54 (exact) |
| 1 foot | meters | 0.3048 (exact) |
| 1 kilogram | pounds | 2.204623 |
| 1 pound | kilograms | 0.45359237 (exact) |
| 1 US gallon | liters | 3.785412 |
| 1 liter | US gallons | 0.264172 |
| 1 ounce | grams | 28.349523 |
| 1 mph | km/h | 1.609344 (exact) |
How do you use the Unit Converter?
- Pick the category.
- Enter a value and source unit.
- Pick the target unit.
Worked example
| Scenario | 5 miles to km |
| Calculation | 5 × 1.60934 |
| Result | 8.0467 km. |
Common use cases
Tips & best practices
Always sanity-check temperature conversions — sign errors are common.
Frequently asked questions
1 mile equals exactly 1.609344 kilometers. The factor has been exact since the 1959 International Yard and Pound Agreement defined the yard as 0.9144 m, making the mile (1,760 yards) exactly 1,609.344 m. Going the other way, 1 km is about 0.621371 miles, so a 10 km run is roughly 6.2 miles and a marathon (42.195 km) is 26.219 miles.
1 kilogram equals approximately 2.20462 pounds. The exact relationship runs the other way: 1 pound is defined as exactly 0.45359237 kg, so the kg-to-lb factor (1 / 0.45359237) is a non-terminating decimal that gets rounded. Quick examples: 70 kg is about 154.3 lb, and a 5 lb bag of flour is about 2.27 kg.
Multiply by 9/5 and add 32: °F = °C × 1.8 + 32. So 20 °C = 68 °F, 37 °C (body temperature) = 98.6 °F, and 100 °C (boiling water) = 212 °F. To go back, subtract 32 first, then multiply by 5/9. The two scales cross at −40, the only temperature where °C and °F read the same.
Exactly 2.54 centimeters — the inch has been defined as 25.4 mm since 1959, so this factor is not an approximation. From it follow the other length factors: 1 foot = 30.48 cm, 1 yard = 0.9144 m, and 1 mile = 1.609344 km. To convert a 15.6-inch laptop screen, multiply: 15.6 × 2.54 = 39.624 cm.
It depends on the gallon. The US gallon is exactly 3.785411784 liters; the imperial (UK) gallon is exactly 4.54609 liters — about 20% larger. That is why UK miles-per-gallon figures look better than US ones for the same car. A US quart is 0.946 L, and a US fluid ounce is 29.5735 mL versus 28.4131 mL for the imperial fluid ounce.
Most everyday factors are exact by definition: 1 inch = 25.4 mm, 1 lb = 0.45359237 kg, 1 US gallon = 3.785411784 L. Approximation only enters when the inverse is a non-terminating decimal (1 kg = 2.2046226218... lb) and gets rounded for display. Temperature conversions are exact formulas, and all SI-to-SI conversions are exact powers of ten.