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Unit Converter — Free Online ToolHow unit conversion works
Every unit conversion is a multiplication. Each unit has a conversion factor relative to a base unit. To convert from unit A to unit B:
Value in B = Value in A × (Factor of A ÷ Factor of B)
For example, to convert 5 km to miles: 1 km = 1000 m; 1 mile = 1609.34 m. So 5 km = 5 × (1000 ÷ 1609.34) = 3.107 miles.
Our Unit Converter does this calculation instantly for all 6 converter types below.
Length conversions
The metric system is based on the meter (m). The imperial system uses inches, feet, yards and miles.
| From | To | Multiply by |
|---|---|---|
| kilometers (km) | miles (mi) | 0.621371 |
| miles (mi) | kilometers (km) | 1.60934 |
| meters (m) | feet (ft) | 3.28084 |
| feet (ft) | meters (m) | 0.3048 |
| centimeters (cm) | inches (in) | 0.393701 |
| inches (in) | centimeters (cm) | 2.54 |
Quick tip: 1 inch = exactly 2.54 cm (this is the exact legal definition). Everything else follows from there.
Weight conversions
The metric base unit is the kilogram (kg). Imperial weight uses pounds and ounces; the stone (14 lbs) is used in the UK and Ireland for body weight.
| From | To | Multiply by |
|---|---|---|
| kilograms (kg) | pounds (lb) | 2.20462 |
| pounds (lb) | kilograms (kg) | 0.453592 |
| kilograms (kg) | ounces (oz) | 35.274 |
| grams (g) | ounces (oz) | 0.035274 |
| metric tons (t) | short tons (US) | 1.10231 |
Use our Weight Converter for any combination including stone.
Speed conversions
Speed is most often expressed as km/h (metric), mph (imperial), m/s (physics), or knots (navigation and aviation).
| From | To | Multiply by |
|---|---|---|
| km/h | mph | 0.621371 |
| mph | km/h | 1.60934 |
| m/s | km/h | 3.6 |
| km/h | knots (kn) | 0.539957 |
| Mach (at sea level) | km/h | 1225.04 |
Volume conversions
The metric base unit for volume is the liter (L). The US customary system uses fluid ounces, cups, pints, quarts and gallons — which differ from UK imperial measures.
| From | To | Multiply by |
|---|---|---|
| liters (L) | US gallons (gal) | 0.264172 |
| US gallons (gal) | liters (L) | 3.78541 |
| liters (L) | US fluid ounces (fl oz) | 33.814 |
| milliliters (mL) | US fluid ounces (fl oz) | 0.033814 |
| US cups | milliliters (mL) | 236.588 |
Area conversions
Area units are the squares of length units. The hectare (ha = 10,000 m²) and acre are used in land measurement.
| From | To | Multiply by |
|---|---|---|
| square meters (m²) | square feet (ft²) | 10.7639 |
| hectares (ha) | acres (ac) | 2.47105 |
| acres (ac) | hectares (ha) | 0.404686 |
| square kilometers (km²) | square miles (mi²) | 0.386102 |
Data storage — decimal GB vs binary GiB
Data storage uses two competing standards that are often confused:
- Decimal (SI): 1 KB = 1,000 bytes · 1 MB = 1,000,000 bytes · 1 GB = 1,000,000,000 bytes. Used by hard drive manufacturers.
- Binary (IEC): 1 KiB = 1,024 bytes · 1 MiB = 1,048,576 bytes · 1 GiB = 1,073,741,824 bytes. Used by operating systems when reporting file sizes.
This is why a "1 TB" drive appears as roughly 931 GiB in Windows — the drive is 1,000,000,000,000 bytes, but Windows divides by 1024³ to get GiB, not by 1000³.
| Decimal | Bytes | Binary equiv. |
|---|---|---|
| 1 KB | 1,000 | 0.977 KiB |
| 1 MB | 1,000,000 | 0.954 MiB |
| 1 GB | 1,000,000,000 | 0.931 GiB |
| 1 TB | 1,000,000,000,000 | 0.909 TiB |
Frequently asked questions
How do I convert km to miles?
Multiply by 0.621371. So 10 km = 6.21 miles. To go the other way, multiply miles by 1.60934. Use our Length Converter for instant results.
How do I convert kg to lbs?
Multiply kilograms by 2.20462. So 70 kg = 154.3 lbs. To go from lbs to kg, multiply by 0.453592.
What is the difference between GB and GiB?
1 GB = 1 billion bytes (decimal). 1 GiB = 1,073,741,824 bytes (binary, powers of 2). Hard drives are sold in GB; operating systems often display GiB. A "1 TB" drive shows as ~931 GiB in Windows — same number of bytes, different prefix.
How do I convert Celsius to Fahrenheit?
°F = (°C × 9/5) + 32. For example: 20°C = (20 × 1.8) + 32 = 68°F. Use our Temperature Converter for any temperature unit including Kelvin.
Conclusion
All unit conversions reduce to a single multiplication by a conversion factor. Once you know the factor between two units, you can convert in either direction instantly. Our free Unit Converter covers all six major categories — length, weight, speed, volume, area and data storage — with metric, imperial and binary units in one place.
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