Electrical Units and Metric Prefixes



A unit of measurement can be defined as a quantity chosen as a standard in terms of which other quantities may be expressed.

Engineering is an applied science dealing with a variety of physical quantities (a physical quantity is one which can be measured) like time, speed, voltage, resistance etc. Hence, for the measurement of these quantities standard units are defined.

There are a number of electrical units defined which are based on the SI system of units.

Standard Electrical Units of Measurement

Electrical Quantity Symbol for Quantity Measuring Unit Symbol for Unit
Charge Q or q Coulomb C
Voltage V or v Volt V
EMF E or e Volt V
Current I or i Ampere A
Resistance R or r Ohm Ω
Inductance L Henry H
Capacitance C Farad F
Conductance G Mho or Siemen ? or Ω-1or S
Power P Watt W
Frequency f Hertz Hz
Impedance Z Ohm Ω

Other Units for Electrical Measurement

Electrical Quantity Symbol for Quantity Measuring Unit Symbol for Unit
Electrical Energy W or E Watt – Hour Wh
Phase Angle θ Degree or Radian ° or Rad
Angular Frequency ω Radian/ Second Rad/s
Time Period T Second s
Time Constant τ Second s

Multiples and their Metric Prefixes

In electrical and electronics engineering, a wide range of values are encountered between maximum and minimum values of a standard electrical unit. Hence, when the quantities being measured are very large or very small, then multiples of the electrical measuring units are used by placing a prefix with the unit.

Metric Prefix Symbol Multiplier Power of Ten
yotta Y 1,000,000,000,000,000,000,000,000 1024
zetta Z 1,000,000,000,000,000,000,000 1021
exa E 1,000,000,000,000,000,000 1018
peta P 1,000,000,000,000,000 1015
tera T 1,000,000,000,000 1012
giga G 1,000,000,000 109
mega M 1,000,000 106
kilo k 1000 103
hecto h 100 102
deca da 10 101
deci d 1/10 10-1
centi c 1/100 10-2
milli m 1/1000 10-3
micro μ 1/1,000,000 10-6
nano n 1/1,000,000,000 10-9
pico p 1/1,000,000,000,000 10-12
femto f 1/1,000,000,000,000,000 10-15
atto a 1/1,000,000,000,000,000,000 10-18
zepto z 1/1,000,000,000,000,000,000,000 10-21
yocto y 1/1,000,000,000,000,000,000,000,000 10-24


Updated on: 2021-05-29T15:37:05+05:30

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