Units of Measurement: The Complete List

Across labs, kitchens, and construction sites, units shape how we measure and compare the world around us. Practical knowledge of common and obscure measures helps whether you’re checking a recipe, sizing a beam, or reading a data sheet.

There are 98 Units of Measurement, ranging from British thermal unit to zetta. For each entry, Symbol,Quantity measured,SI equivalent are listed to make conversions and comparisons straightforward — you’ll find below.

How can I convert values between the units listed?

Use the SI equivalent column as your starting point: convert the original amount to the SI value (usually by multiplying or dividing by the given factor), then convert from SI to your target unit. For non-SI units like the British thermal unit you may need a fixed conversion constant; the SI equivalent provided eliminates guesswork.

Are all the items on this list part of the SI system?

No — the list mixes SI units and widely used non-SI units and prefixes (for example, zetta is an SI prefix while the British thermal unit is non-SI). The SI equivalent column clarifies how each relates to the SI system so you can compare and convert consistently.

Units of Measurement

Name	Symbol	Quantity measured	SI equivalent
metre	m	length	1 m
kilogram	kg	mass	1 kg
second	s	time	1 s
ampere	A	electric current	1 A
kelvin	K	thermodynamic temperature	1 K
mole	mol	amount of substance	1 mol
candela	cd	luminous intensity	1 cd
radian	rad	plane angle	1 rad
steradian	sr	solid angle	1 sr
hertz	Hz	frequency	1 s^-1
newton	N	force	1 kg·m/s^2
pascal	Pa	pressure	1 N/m^2
joule	J	energy/work	1 N·m
watt	W	power	1 J/s
coulomb	C	electric charge	1 A·s
volt	V	electric potential	1 J/C
ohm	Ω	electrical resistance	1 V/A
siemens	S	electrical conductance	1 A/V
farad	F	capacitance	1 C/V
henry	H	inductance	1 Wb/A
tesla	T	magnetic flux density	1 Wb/m^2
weber	Wb	magnetic flux	1 V·s
lumen	lm	luminous flux	1 cd·sr
lux	lx	illuminance	1 lm/m^2
becquerel	Bq	radioactivity (decays/s)	1 s^-1
gray	Gy	absorbed dose	1 J/kg
sievert	Sv	dose equivalent	1 J/kg
katal	kat	catalytic activity	1 mol/s
degree Celsius	°C	temperature	T(K)=T(°C)+273.15; 1 °C=1 K
degree (angle)	°	plane angle	π/180 rad
minute	min	time	60 s
hour	h	time	3,600 s
day	d	time	86,400 s
yotta	Y	prefix (multiplier)	10^24 (dimensionless)
zetta	Z	prefix (multiplier)	10^21 (dimensionless)
exa	E	prefix (multiplier)	10^18 (dimensionless)
peta	P	prefix (multiplier)	10^15 (dimensionless)
tera	T	prefix (multiplier)	10^12 (dimensionless)
giga	G	prefix (multiplier)	10^9 (dimensionless)
mega	M	prefix (multiplier)	10^6 (dimensionless)
kilo	k	prefix (multiplier)	1,000 (dimensionless)
hecto	h	prefix (multiplier)	10^2 (100) (dimensionless)
deca	da	prefix (multiplier)	10^1 (10) (dimensionless)
deci	d	prefix (multiplier)	10^-1 (dimensionless)
centi	c	prefix (multiplier)	10^-2 (dimensionless)
milli	m	prefix (multiplier)	10^-3 (dimensionless)
micro	µ	prefix (multiplier)	10^-6 (dimensionless)
nano	n	prefix (multiplier)	10^-9 (dimensionless)
pico	p	prefix (multiplier)	10^-12 (dimensionless)
femto	f	prefix (multiplier)	10^-15 (dimensionless)
atto	a	prefix (multiplier)	10^-18 (dimensionless)
zepto	z	prefix (multiplier)	10^-21 (dimensionless)
yocto	y	prefix (multiplier)	10^-24 (dimensionless)
inch	in	length	0.0254 m
foot	ft	length	0.3048 m
yard	yd	length	0.9144 m
mile	mi	length	1,609.34 m
chain	ch	length	20.12 m
furlong	fur	length	201.17 m
nautical mile	NM	length	1,852 m
knot	kn	speed	0.51 m/s
acre	ac	area	4,046.86 m^2
square mile	mi^2	area	2.59 km^2
gallon (US)	gal (US)	volume	3.79 L
gallon (UK)	gal (UK)	volume	4.55 L
pint (US)	pt (US)	volume	0.47 L
pint (UK)	pt (UK)	volume	0.57 L
fluid ounce (US)	fl oz (US)	volume	0.03 L
ounce (avoirdupois)	oz	mass	28.35 g
pound	lb	mass	0.45 kg
ton (short)	ton (US)	mass	907.18 kg
stone	st	mass	6.35 kg
barrel (oil)	bbl	volume	158.99 L
liter	L	volume	0.001 m^3
tonne	t	mass	1,000 kg
hectare	ha	area	10,000 m^2
electronvolt	eV	energy	1.60e-19 J
atomic mass unit	u	mass	1.66e-27 kg
angstrom	Å	length	1.00e-10 m
barn	b	area	1.00e-28 m^2
erg	erg	energy	1.00e-7 J
dyne	dyn	force	1.00e-5 N
calorie	cal	energy	4.18 J
kilocalorie	kcal	energy	4,184 J
British thermal unit	BTU	energy	1,055.06 J
horsepower	hp	power	745.70 W
atmosphere	atm	pressure	101,325 Pa
bar	bar	pressure	100,000 Pa
torr	Torr	pressure	133.32 Pa
curie	Ci	radioactivity	37,000,000,000 Bq
rem	rem	radiation dose	0.01 Sv
parsec	pc	length	3.09e16 m
light-year	ly	length	9.46e15 m
astronomical unit	au	length	149,597,870,700 m
slug	slug	mass	14.59 kg
grain	gr	mass	64.80 mg
troy ounce	oz t	mass	31.10 g
carat	ct	mass	0.20 g

Images and Descriptions

metre

The metre is the SI base unit of length, defined by the distance light travels in a vacuum in 1/299,792,458 s. It’s the global standard for measuring distances from everyday lengths to scientific experiments.

kilogram

The kilogram is the SI base unit of mass, now defined by the Planck constant. It’s used worldwide for commerce, science and engineering; common reference for body mass and packaged goods.

second

The second is the SI base unit of time, defined by vibrations of a cesium atom. It underpins clocks, timing systems, and scientific measurements from electronics to astronomy.

ampere

The ampere is the SI base unit of electric current, defined by the elementary charge and quantum standards. It’s the basic measure for electrical circuits, power systems and device specifications.

kelvin

The kelvin is the SI base unit for thermodynamic temperature, anchored to fixed physical constants. Used in science and engineering to describe absolute temperature and thermal behavior.

mole

The mole is the SI base unit for amount of substance, exactly 6.02214076×10^23 specified entities. It’s fundamental in chemistry for counting atoms, molecules and reactions.

candela

The candela is the SI base unit for luminous intensity in a given direction. It’s used in lighting, display brightness and photometric specifications to quantify perceived light.

radian

The radian is the SI derived unit of plane angle: arc length divided by radius. It’s the natural angular unit in mathematics, physics and engineering for rotational measures.

steradian

The steradian is the SI derived unit of solid angle, the 3D analogue of the radian. It’s used in radiometry, astronomy and lighting to describe portions of a sphere.

hertz

The hertz measures cycles per second — frequency of periodic events such as waves, AC electricity, or clock ticks. It’s essential in audio, radio, and signal processing.

newton

The newton is the SI unit of force: one kilogram accelerated at one metre per second squared. It’s used in mechanics for weight, thrust and structural loads.

pascal

The pascal is the SI unit of pressure: one newton of force per square metre. Common in physics, meteorology, engineering and material stress measurements.

joule

The joule is the SI unit of energy and work: one newton moved through one metre. It measures mechanical, electrical and thermal energy in everyday and scientific contexts.

watt

The watt quantifies power — energy per unit time. One watt is one joule per second and it’s used for lightbulbs, engines, electronics and heat output ratings.

coulomb

The coulomb measures electric charge: one ampere of current over one second. It’s the basic unit for charge in circuits, electrochemistry and particle counts.

volt

The volt is the SI unit of electric potential difference and electromotive force. It describes battery voltages, mains supply and signal levels in electronics.

ohm

The ohm measures electrical resistance: one volt of potential per ampere of current. It’s fundamental in circuit design, component ratings and impedance calculations.

siemens

The siemens is the inverse of resistance, measuring conductance. It helps quantify how easily current flows through materials or components in electrical engineering.

farad

The farad measures capacitance: one coulomb stored per volt. Capacitor values in electronics, energy storage and signal filtering are expressed in farads or fractions thereof.

henry

The henry quantifies inductance: one weber of magnetic flux per ampere. Used in coils, transformers and radio circuits for energy storage and magnetic coupling.

tesla

The tesla is the SI unit of magnetic flux density. It measures magnetic field strength in MRI machines, particle accelerators and magnet technology.

weber

The weber quantifies magnetic flux through a surface: one volt-second. It’s important in electromagnetism, generators and magnetic circuit calculations.

lumen

The lumen measures perceived light output integrated over a solid angle. It’s used to rate lamps, LEDs and lighting fixtures for human vision.

lux

The lux measures illumination on a surface: lumens per square metre. It describes brightness conditions for workplaces, photography and building lighting design.

becquerel

The becquerel measures radioactive decay rate: one nuclear disintegration per second. It’s the SI unit for radioactivity in nuclear medicine, safety and research.

gray

The gray measures absorbed radiation dose: one joule of energy deposited per kilogram. Used in radiotherapy, radiation protection and dosimetry.

sievert

The sievert quantifies biological effect of radiation exposure, combining absorbed dose with weighting factors. It’s central to radiation safety and health guidelines.

katal

The katal measures catalytic activity: one mole of substrate transformed per second. It’s used in enzymology and chemical reaction engineering.

degree Celsius

Degree Celsius is a temperature scale offset from kelvin; temperature differences match kelvin. Common for weather, cooking and daily temperatures worldwide.

degree (angle)

The degree divides a circle into 360 equal parts. It’s a widely used angular unit in navigation, mapping and everyday geometry, convertible exactly to radians.

minute

The minute is a non‑SI time unit of 60 seconds. Widely used for everyday timekeeping, schedules and durations; officially accepted for use with SI.

hour

The hour equals 3,600 seconds (60 minutes). It’s the standard human‑scale time unit for daily life, work schedules and many engineering time calculations.

day

The day is 24 hours or 86,400 seconds, based on Earth’s rotation. It’s used universally for calendars, long-term scheduling and astronomical timekeeping.

yotta

Yotta is the largest SI prefix, multiplying a unit by 10^24. It’s used for astronomical data, global storage metrics and describing extremely large quantities.

zetta

Zetta multiplies a unit by 10^21. Common in data measurement (zettabytes) and physics when discussing very large scales.

exa

Exa is 10^18, used in computing (exaflops, exabytes) and scientific contexts for vast quantities such as particle counts or energy scales.

peta

Peta represents 10^15. It appears in data storage (petabyte) and large-scale computations or measurements in science and engineering.

tera

Tera denotes 10^12. Common in computing (terabyte), physics and engineering for large but human‑scale quantities.

giga

Giga is 10^9, used for frequencies (gigahertz), data (gigabyte) and large measurements in technology and science.

mega

Mega denotes one million (10^6). Common in power (megawatt), computing (megabyte historically) and engineering scales.

kilo

Kilo multiplies a unit by 1,000. It’s the most familiar prefix for everyday weights (kilogram), distances (kilometre) and many metrics.

hecto

Hecto is 100 times a unit; less common today but appears in hectopascal for air pressure and historical measurements.

deca

Deca multiplies by ten; rarely used but seen in decametre for large‑scale topography and some engineering contexts.

deci

Deci divides a unit by ten (0.1). Mostly used in metric subdivisions like decilitres in some countries and educational contexts.

centi

Centi denotes one‑hundredth (0.01). Familiar from centimetre and centilitre, common in daily measurements and consumer contexts.

milli

Milli means one‑thousandth (0.001). It’s ubiquitous in measurements like millimetre, millilitre and milligram across science and everyday life.

micro

Micro denotes one‑millionth (10^-6). Widely used in electronics (microfarad), biology (micrometre) and precision measurements.

nano

Nano is one‑billionth (10^-9). Central to nanotechnology, semiconductor specifications and tiny-scale measurements.

pico

Pico denotes 10^-12 and appears in physics, electronics and timing measurements for very small quantities.

femto

Femto is 10^-15, used in ultrafast physics and measuring extremely small timescales or quantities.

atto

Atto equals 10^-18, relevant in quantum physics, particle counts and very small measured values.

zepto

Zepto denotes 10^-21, used rarely except in specialized scientific notation for minuscule scales.

yocto

Yocto is 10^-24, the smallest standard SI prefix used for describing extraordinarily small quantities in physics and chemistry.

inch

The inch is an imperial/U.S. customary length unit exactly 0.0254 metres. Common in North America, construction and manufacturing for small measurements.

foot

The foot (0.3048 m exactly) is used in the U.S. and UK construction, aviation altitude (feet), and everyday height measurements in some countries.

yard

The yard equals 0.9144 metres exactly. It’s used in textiles, sports fields (some contexts) and older measuring systems.

mile

The (statute) mile is 1,609.344 metres exactly. Common in the U.S. and UK for road distances and travel measurements.

chain

The survey chain (66 ft) equals 20.1168 metres exactly. Historically used in land surveying; still appears in cadastral records and older maps.

furlong

The furlong is 201.168 metres exactly (10 chains). Historically used in horse racing and land measurement; now rare but still referenced.

nautical mile

The nautical mile is exactly 1,852 metres, based on Earth’s geometry. It’s standard in maritime and aviation navigation.

knot

The knot is one nautical mile per hour; about 0.51 m/s. It’s the standard speed unit for ships and aircraft.

acre

The acre is 4,046.8564224 square metres (commonly 4,046.86 m^2), used for land area in the U.S., UK and former British territories.

square mile

The square mile covers 2.59 square kilometres (approx). It’s used for large land areas, municipalities and geographical statistics.

gallon (US)

The U.S. gallon is about 3.78541 litres (rounded 3.79 L). Widely used in the United States for fuel, beverages and liquid volumes.

gallon (UK)

The imperial (UK) gallon equals 4.54609 litres (rounded 4.55 L). Used historically in Britain and still in certain Commonwealth contexts.

pint (US)

The U.S. pint is 473.176 mL (0.47 L), used for beverages and liquid measures in the United States.

pint (UK)

The UK (imperial) pint is 568.261 mL (0.57 L), commonly used for beer and milk measures in Britain and Ireland.

fluid ounce (US)

The U.S. fluid ounce equals about 29.57 mL (0.03 L). It’s used in recipes, packaging and small‑volume liquid measurements.

ounce (avoirdupois)

The avoirdupois ounce is 28.34952 grams, commonly used for food packaging, postal weights and everyday mass in the U.S. and UK.

pound

The avoirdupois pound equals 0.45359237 kilograms (rounded 0.45 kg). It’s widely used in the U.S. for body weight and commerce.

ton (short)

The short ton (U.S.) equals 907.18474 kilograms (rounded 907.18 kg). Used in North American industry and shipping tonnage.

stone

The stone is 14 pounds or 6.35029318 kilograms (rounded 6.35 kg). Common in the UK and Ireland for body weight reporting.

barrel (oil)

The (U.S.) oil barrel is 158.9873 litres (rounded 158.99 L). It’s a standard commercial unit in the petroleum industry.

liter

The litre is a non‑SI unit accepted for use with SI: one cubic decimetre (0.001 m^3). It’s the common unit for liquids worldwide.

tonne

The tonne (metric ton) is exactly 1,000 kilograms. Widely used in shipping, resource reporting and international trade.

hectare

The hectare equals 10,000 square metres and is commonly used for land area, agriculture and property sizes around the world.

electronvolt

The electronvolt is the energy gained by an electron across one volt, 1.602×10^-19 J. It’s fundamental in atomic, particle and condensed‑matter physics.

atomic mass unit

The unified atomic mass unit (dalton) is about 1.6605×10^-27 kg, defined from carbon-12. It’s used to express atomic and molecular masses.

angstrom

The ångström is 10^-10 metres, convenient for atomic and molecular scales such as bond lengths and crystal lattice spacings; widely used in chemistry and crystallography.

barn

The barn is 10^-28 square metres, a unit in nuclear and particle physics for cross-sectional area; its whimsical name makes it memorable in nuclear measurements.

erg

The erg is a CGS energy unit equal to 10^-7 joules. It appears in older physics literature and astrophysics for small energy scales.

dyne

The dyne is the CGS unit of force: 10^-5 newtons. It’s used historically in mechanics and some physics contexts that employ CGS units.

calorie

The calorie (thermochemical) is 4.184 joules. It’s known from chemistry and nutrition (though food calories are kilocalories).

kilocalorie

The kilocalorie (often called Calorie in food) equals 1,000 calories or 4,184 joules. It’s used to express food energy and metabolic intake.

British thermal unit

The BTU measures thermal energy; one BTU equals about 1,055.06 joules. It’s used in heating, ventilation and air conditioning (HVAC) ratings.

horsepower

Mechanical horsepower is approximately 745.7 watts. Used historically for engines and still common in automotive and machinery power ratings.

atmosphere

The standard atmosphere is 101,325 pascals, a conventional pressure unit used in meteorology, aviation and earlier scientific literature.

bar

The bar equals 100,000 pascals exactly, a convenient atmospheric scale used in meteorology, diving and engineering.

torr

The torr is defined as 1/760 of standard atmosphere, about 133.322 Pa (rounded 133.32 Pa). Used in vacuum physics and low‑pressure measurements.

curie

The curie is an older radioactivity unit equal to 3.7×10^10 becquerels (37,000,000,000 decays per second), still cited historically and in nuclear medicine.

rem

The rem is an older unit of radiation dose equivalent: one rem equals 0.01 sievert. It’s seen in radiological protection contexts and older regulations.

parsec

The parsec is about 3.09×10^16 metres, the astronomical distance at which one astronomical unit subtends one arcsecond. Common in astrophysics and galactic scales.