Units & Conversions

Units & Conversions#

Reference of SI base units, derived units, common non-SI units, prefixes, and conversion factors operators reach for in physical measurements, scientific reporting, and cross-system work.

SI base units#

Quantity

Unit

Symbol

Length

meter

m

Mass

kilogram

kg

Time

second

s

Electric current

ampere

A

Temperature

kelvin

K

Amount of substance

mole

mol

Luminous intensity

candela

cd

SI derived units#

Quantity

Unit

Symbol

Definition

Frequency

hertz

Hz

1/s

Force

newton

N

kg·m/s²

Pressure

pascal

Pa

N/m²

Energy / work

joule

J

N·m = kg·m²/s²

Power

watt

W

J/s

Electric charge

coulomb

C

A·s

Voltage

volt

V

W/A

Capacitance

farad

F

C/V

Resistance

ohm

Ω

V/A

Conductance

siemens

S

A/V = 1/Ω

Magnetic flux

weber

Wb

V·s

Magnetic flux dens.

tesla

T

Wb/m²

Inductance

henry

H

Wb/A

Lux (illuminance)

lux

lx

cd·sr/m²

Activity (radio)

becquerel

Bq

1/s (decay)

Absorbed dose

gray

Gy

J/kg

Equivalent dose

sievert

Sv

J/kg (weighted)

Catalytic activity

katal

kat

mol/s

Plane angle

radian

rad

m/m

Solid angle

steradian

sr

m²/m²

Celsius temp.

degree Celsius

°C

K - 273.15

SI prefixes#

Prefix

Sym.

Factor

quetta

Q

10^30

ronna

R

10^27

yotta

Y

10^24

zetta

Z

10^21

exa

E

10^18

peta

P

10^15

tera

T

10^12

giga

G

10^9

mega

M

10^6

kilo

k

10^3

hecto

h

10^2

deca / deka

da

10^1

deci

d

10^-1

centi

c

10^-2

milli

m

10^-3

micro

µ

10^-6

nano

n

10^-9

pico

p

10^-12

femto

f

10^-15

atto

a

10^-18

zepto

z

10^-21

yocto

y

10^-24

ronto

r

10^-27

quecto

q

10^-30

Binary prefixes (IEC 60027-2 / ISO 80000-13):

Prefix

Sym.

Factor

kibi

Ki

2^10 = 1,024

mebi

Mi

2^20

gibi

Gi

2^30

tebi

Ti

2^40

pebi

Pi

2^50

exbi

Ei

2^60

zebi

Zi

2^70

yobi

Yi

2^80

Length / distance#

Conversion

Factor

1 inch

25.4 mm exactly.

1 foot

0.3048 m exactly.

1 yard

0.9144 m.

1 mile (statute)

1609.344 m.

1 nautical mile

1852 m exactly (international).

1 nautical mile

1853.18 m (US survey, deprecated).

1 league (land)

~4828 m (3 miles).

1 league (sea)

~5556 m (3 nautical miles).

1 fathom

1.8288 m.

1 angstrom (Å)

1e-10 m.

1 light-year

9.461e15 m.

1 parsec

3.086e16 m = 3.262 ly.

1 AU

1.496e11 m.

Mass#

Conversion

Factor

1 ounce (avdp)

28.3495 g.

1 pound (avdp)

453.592 g.

1 stone (UK)

6.35029 kg.

1 short ton (US)

907.185 kg.

1 long ton (UK)

1016.05 kg.

1 metric tonne (t)

1000 kg.

1 troy ounce

31.1035 g.

1 carat (gem)

200 mg.

1 grain

64.799 mg.

Volume#

Conversion

Factor

1 liter

0.001 m³ = 1000 cm³.

1 US fluid oz

29.5735 mL.

1 imperial fl oz

28.4131 mL.

1 US cup

236.588 mL.

1 US gallon

3.78541 L.

1 imperial gallon

4.54609 L.

1 US barrel (oil)

158.987 L.

1 cubic inch

16.3871 cm³.

1 cubic foot

28.3168 L.

Speed#

Conversion

Factor

1 m/s

2.23694 mph = 3.6 km/h = 1.94384 knots.

1 km/h

0.621371 mph = 0.539957 knots.

1 mph

1.609344 km/h = 0.868976 knots.

1 knot

1.852 km/h = 1.15078 mph (1 nm/h).

1 Mach (15°C)

340.29 m/s.

Temperature#

Formula

Notes

°C → K

K = °C + 273.15

°F → °C

°C = (°F - 32) · 5/9

°C → °F

°F = °C · 9/5 + 32

K → °C

°C = K - 273.15

°Re (Réaumur)

°C × 4/5 (rare).

°R (Rankine)

K × 9/5; absolute Fahrenheit.

Energy / power#

Conversion

Factor

1 calorie (thermo)

4.184 J.

1 kilocalorie

4184 J = 4.184 kJ (“Calorie”, food label).

1 BTU (Int’l)

1055.06 J.

1 kWh

3.6 MJ.

1 erg

1e-7 J.

1 electron-volt

1.602176634e-19 J.

1 horsepower (mech)

745.7 W.

1 horsepower (metr.

) 735.5 W.

1 ton refrigeration

3516 W.

1 quad

1e15 BTU = 1.055 EJ.

Pressure#

Conversion

Factor

1 atm (standard)

101,325 Pa exactly.

1 bar

100,000 Pa.

1 mbar

100 Pa = 1 hPa.

1 psi

6894.76 Pa.

1 mmHg / Torr

133.322 Pa.

1 inHg

3386.39 Pa.

Information#

Conversion

Notes

1 byte

8 bits.

1 kB / KiB

1000 B / 1024 B (decimal vs binary).

1 MB / MiB

1e6 B / 2^20 B.

1 GB / GiB

1e9 B / 2^30 B.

1 TB / TiB

1e12 B / 2^40 B.

1 baud

symbols per second (not always = bits/s).

1 nibble

4 bits.

Logarithmic units#

Unit

Notes

dB

10 log₁₀(P₁/P₂) (power) or 20 log₁₀(V₁/V₂) (voltage).

dBm

dB referenced to 1 mW.

dBW

dB referenced to 1 W.

dBV

dB referenced to 1 V.

dBµV

dB referenced to 1 µV.

dBi / dBd

antenna gain re. isotropic / dipole.

dB SPL

sound pressure re. 20 µPa.

neper (Np)

ln(V₁/V₂); 1 Np = 8.686 dB.

Astronomy / radio#

Quantity

Notes

Wavelength λ

c / f; c ≈ 3×10⁸ m/s.

λ at 1 GHz

~30 cm.

λ at 2.4 GHz

~12.5 cm (Wi-Fi 2.4).

λ at 5 GHz

~6 cm (Wi-Fi 5).

λ at 1090 MHz

~27.5 cm (ADS-B).

1 light-second

299,792,458 m.

1 parsec

3.086e16 m = 3.262 ly = 206,265 AU.

1 magnitude

factor ~2.512 in brightness.

References#

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