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
Unit
Name
Preset
nmi
nautical miles
sea mile
sea miles
cable (intl)
cables (international)
cable (US)
cables (US)
fathom
fathoms
league (naut)
nautical leagues
km
kilometres (cross-conversion)
m
metres (cross-conversion)
mi
miles (cross-conversion)
ft
feet (cross-conversion)
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.