Physical Quantities (Electrical), Symbols and Units

Quantity

Symbol

Unit

Abbreviation of Unit after Numerical Value

Force

F

newton

N

Work

or

Energy

W

joule

or

newton metre

J

or

Nm

Torque

T

newton metre

Nm

Power

P

watt

W

Time

t

second

s

Angular Velocity

w

radians per second

rad/s

Speed

N

revolutions per minute

rev/min

(sometimes r.p.m.)

n

revolutions per second

rev/s

(sometimes r.p.s.)

Electric Charge

Q

coulomb

C

Potential Difference (p.d.)

V

volt

V

Electromotive force (e.m.f.)

E

volt

V

Current

I

ampere

A

Resistance

R

ohm

W

Resistivity

(specific resistance)

r (rho)

ohm metre

Wm

Conductance

G

siemens

S

Magnetomotive force (m.m.f.)

F

ampere-turn

At

Magnetic field strength

H

ampere-turn per metre or ampere per metre

At/m or

A/m

Magnetic flux

f (phi)

weber

Wb

Magnetic flux density

B

tesla

T

Reluctance

S

ampere-turn or ampere per weber

At/Wb or A/Wb

Absolute permeability of free space

m0 (mu)

henry per metre

H/m

Absolute permeability

m

henry per metre

H/m

Relative permeability

mr

-

-

Self inductance

L

henry

H

Mutual inductance

M

henry

H

Reactance

X

ohm

W

Impedance

Z

ohm

W

Frequency

F

hertz

Hz

Capacitance

C

farad

F

Absolute permittivity of free space

e0 (epsilon)

farad per metre

F/m

Absolute permittivity

e

farad per metre

F/m

Relative permittivity (dielectric constant, specific inductive capacity)

er

-

-

Electric field strength, electric force

-

volts per metre

V/m

Electric flux

Y (psi)

coulomb

C

Electric flux density, electric displacement

D

coulomb per square metre

C/m2

Active power

P

watt

W

Reactive power

Q

volt ampere reactive

VAr

Apparent power

S

volt ampere

VA

Phase difference

f (phi)

degree

0

Power factor (p.f.)

Cos f

-

-

 


Conversion into SI Units

To Convert

Multiply by

Conversely Multiply by

Distance

inches millimetres

25.400

0.0394

inches centimetres

2.540

0.3937

feet metres

0.3048

3.2808

yards metres

0.914

1.094

miles kilometres

1.6093

0.621

nautical miles kilometres

1.852

0.539

nautical miles metres

1852

0.0005399

fathom m

1.8228

0.5487

micron metre

10-6

106

Area

square inches square millimetres

645.16

15.50

square inches square centimetres

6.4516

0.1550

square feet square metres

0.0929

10.764

Volume

cubic inches cubic centimetres

16.387

0.061

cubic feet cubic metres

0.02832

35.315

gallons litres (1 litre = 1 cubic decimetre)

4.546

0.220

gallons m3

4.546 x 10-3

219.9

litre m3

10-3

103

pint m3

0.568 x 10-3

1760.5

quart m3

1.136 x 10-3

879.9

ocean tons cubic metres

1.132

0.883

gallons/minute m3/h

0.273

3.666

Velocity

feet/s m/s

0.3048

3.281

miles/h km/h

1.609

0.6215

knots (nautical mile per hour) m/s

0.5144

1.943

mile/h m/s

0.447

 

Mass

gram kg

10-3

103

pound (lbm) kg

0.45359237

2.2046

slug kg

14.59

0.0685

ton kg

1016

0.9842 x 10-3

tonne (metric) kg

103

10-3

tons tonnes

1.016

0.984

Pressure

tons/in2 kg/mm2

1.575

6.635

dyne/cm2 N/m2

0.1

10

kgf/ cm2 kN/m2

98.07

0.0102

p.s.i. (lbf / inch2) kg/mm2

0.070

14.223

p.s.i. (lbf / inch2) kN/m2

6.89476

0.145

inches of water N/m2

249.5

4.008 x 10-3

feet of water kN/m2

2.989

0.3345

inches of Hg kN/m2

3.386

0.2953

mm of Hg kN/m2

0.1333

7.502

torr mm of Hg

1

1

Pascal (Pa) N/m2

1

1

bar kN/m2

100

0.01

atm kN/m2

101.333

98.69 x 10-3

 

Conversion into SI Units

To Convert

Multiply by

Conversely Multiply by

Density

gram/cm3 kg/m3

103

10-3

pound/foot3 kg/m3

16.02

0.0624

pound/inch3 kg/m3

27.679 x 109

36.123 x 10-12

slug/foot3 kg/m3

515.4

1.94 x 10-3

Force

dyne N

10-5

105

kgf N

9.807

0.102

lbf N

4.44822

0.2248

Energy

Erg J

10-7

107

calorie J

4. 1868

0.2388

foot-pound J

1.356

0.7375

Btu kJ

1.05506

0.9478

Power

erg/second W = Nm/s = J/s

10-7

107

foot-pound/second W

1.356

0.7375

horsepower kW

0.7457

1.341

horsepower W

745.700

1341

horsepower (metric) kW

0.7355

1.360

British h.p. (745.7 w) metric h.p. (735.5w)

1.014

0.986

Discharge

cusecs (ft3/s) m3/s

0.02832

35.33

gpm (gallons / min) m3/s

3.0758 x 103

0.3251 x 10-3

litre/s m3/s

10-3

103

pound/sec kg/s

0.4536

2.204

 

Prefixes, Symbols, Multiples and Sub-multiples of the S.I. System

Prefix

Symbol

Units Multiplying Factor

tetra

T

1012

giga

G

109

mega

M

106

kilo

k

103

hecto

h

102

deca

da

101

deci

d

10-1

centi

c

10-2

milli

m

10-3

micro

m

10-6

nano

n

10-9

pico

p

10-12