Free Online Unit Converter – Length, Area, Energy, Power & More
Free Online Unit Converter to instantly convert length, area, mass, volume, speed, temperature, energy, power, torque, frequency, luminance, data, and nautical units. Includes Quick Presets for popular lookups like hectares to m², nautical miles to km, BTU to kcal, torque N·m to lbf·ft, Hz to rpm, and ppm to mg/m³.
Supported Units
Click “Use this” to prefill the converter with the unit as the From selection.
Length
| Unit | Name | Preset |
|---|---|---|
| m | metres | |
| km | kilometres | |
| cm | centimetres | |
| mm | millimetres | |
| in | inches | |
| ft | feet | |
| yd | yards | |
| mi | miles |
Area
| Unit | Name | Preset |
|---|---|---|
| m² | square metres | |
| ha | hectares | |
| km² | square kilometres | |
| ft² | square feet | |
| acre | acres |
Volume
| Unit | Name | Preset |
|---|---|---|
| L | litres | |
| m³ | cubic metres | |
| mL | millilitres | |
| cL | centilitres | |
| dL | decilitres | |
| gal (US) | US gallons | |
| gal (Imp) | Imperial gallons |
Mass
| Unit | Name | Preset |
|---|---|---|
| kg | kilograms | |
| g | grams | |
| mg | milligrams | |
| lb | pounds | |
| oz | ounces |
Speed
| Unit | Name | Preset |
|---|---|---|
| m/s | metres per second | |
| km/h | kilometres per hour | |
| mph | miles per hour | |
| knot | knots |
Time
| Unit | Name | Preset |
|---|---|---|
| s | seconds | |
| min | minutes | |
| h | hours | |
| day | days |
Temperature
| Unit | Name | Preset |
|---|---|---|
| °C | degrees Celsius | |
| °F | degrees Fahrenheit | |
| K | kelvin | |
| °R | degrees Rankine |
Energy
| Unit | Name | Preset |
|---|---|---|
| J | joules | |
| kJ | kilojoules | |
| cal | calories | |
| kcal | kilocalories | |
| BTU | British thermal units |
Power
| Unit | Name | Preset |
|---|---|---|
| W | watts | |
| kW | kilowatts | |
| hp | horsepower | |
| BTU/h | BTU per hour | |
| kcal/h | kilocalories per hour |
Pressure
| Unit | Name | Preset |
|---|---|---|
| Pa | pascals | |
| kPa | kilopascals | |
| MPa | megapascals | |
| bar | bar | |
| atm | atmospheres | |
| psi | pounds per square inch | |
| mmHg | millimetres of mercury |
Torque
| Unit | Name | Preset |
|---|---|---|
| N·m | newton-metres | |
| lbf·ft | pound-feet | |
| lbf·in | pound-inches | |
| kgf·m | kilogram-force metres |
| Unit | Name | Preset |
|---|---|---|
| Hz | hertz | |
| kHz | kilohertz | |
| MHz | megahertz | |
| GHz | gigahertz | |
| rpm | revolutions per minute | |
| rad/s | radians per second | |
| s (period) | seconds (period) |
Luminance
| Unit | Name | Preset |
|---|---|---|
| cd/m² | candelas per square metre (nits) | |
| nit | nits (alias of cd/m²) | |
| fL | foot-lamberts | |
| cd/ft² | candelas per square foot |
Luminous Efficacy
| Unit | Name | Preset |
|---|---|---|
| lm/W | lumens per watt | |
| % of max | % of theoretical maximum (683 lm/W @ 555 nm) |
Switch SI/IEC via the “Data base” dropdown in the form. The From/To lists will rebuild to show only that family.
Bytes (SI)
| Unit | Name | Preset |
|---|---|---|
| B | Bytes | |
| kB | Kilobytes | |
| MB | Megabytes | |
| GB | Gigabytes | |
| TB | Terabytes | |
| PB | Petabytes | |
| EB | Exabytes | |
| ZB | Zettabytes | |
| YB | Yottabytes |
Bytes (IEC)
| Unit | Name | Preset |
|---|---|---|
| KiB | Kibibytes | |
| MiB | Mebibytes | |
| GiB | Gibibytes | |
| TiB | Tebibytes | |
| PiB | Pebibytes | |
| EiB | Exbibytes | |
| ZiB | Zebibytes | |
| YiB | Yobibytes |
Bits (SI)
| Unit | Name | Preset |
|---|---|---|
| b | bits | |
| kb | kilobits | |
| Mb | megabits | |
| Gb | gigabits | |
| Tb | terabits | |
| Pb | petabits | |
| Eb | exabits | |
| Zb | zettabits | |
| Yb | yottabits |
Bits (IEC)
| Unit | Name | Preset |
|---|---|---|
| Kib | kibibits | |
| Mib | mebibits | |
| Gib | gibibits | |
| Tib | tebibits | |
| Pib | pebibits | |
| Eib | exbibits | |
| Zib | zebibits | |
| Yib | yobibits |
Frequently Asked Questions
It converts length, area (incl. hectares), volume (incl. cL/dL), mass, speed, time, temperature, energy (BTU/kcal), power (BTU/h, kW, hp), torque, pressure, frequency (Hz, rpm, rad/s, period), luminance, luminous efficacy, nautical/geography distances (nautical miles, cables, fathoms, leagues), data (Bytes/Bits up to Yotta/Yobi), and air concentration. Best for quick everyday conversions and engineering lookups.
Pick a Category, then choose From and To units (they show as “symbol (name)”, e.g., km/h (kilometres per hour)), enter a value, and the result appears instantly with both a numeric value and a human-readable unit name. Use the “Swap” button to reverse quickly.
SI uses powers of 1000 (kB, MB, GB…), IEC uses powers of 1024 (KiB, MiB, GiB…). Choose the base from the Data Base dropdown; the From/To lists rebuild so you only see the selected family for both Bytes and Bits.
Yes. The Data category includes both Bytes and Bits in the same list for the chosen base; conversions apply the exact 8:1 ratio and the selected SI or IEC multipliers up to Yotta/Yobi.
Luminance (cd/m², nits, fL, cd/ft²) measures emitted or reflected brightness per area. Luminous Efficacy converts between lm/W and % of the 683 lm/W theoretical maximum—useful for LEDs and lighting efficiency.
The tool renders correct typographic symbols (e.g., m/s, km/h, BTU/h, cd/ft², mg/m³, µg/m³) for clarity and SEO; your selections always show the proper symbol and a descriptive name.
The Nautical Distance category converts between nautical miles (nmi/sea mile), cables (international & US), fathoms, nautical leagues, and cross-converts with km, m, mi, and ft.
Yes. Use “Copy” to copy the numeric value, or “Copy (w/ unit)” to copy a friendly phrase like “3.5 megabytes” for pasting into emails or reports.
Click “Use this” next to any unit; the tool sets the Category and From unit automatically, picks a sensible To unit, and expands the matching accordion section for faster workflows.
Yes. Use the “Decimals” dropdown (0–10). The tool rounds the final result to your selection while preserving precise internal math.
Absolutely. The tool uses standard formulas for °C⇄°F, K, and °R, handling absolute scales correctly.
Yes. Energy supports BTU and kcal; Power supports BTU/h and kcal/h, along with W, kW, and hp for HVAC and appliance sizing comparisons.
Constants and exact factors are used where defined (e.g., in, ft, mi, nmi, BTU/it); temperature and gas conversions apply standard formulas and the ideal gas relation for context-dependent cases.