

Electrical
Formulas,
Power Calculations, Symbols and Equations 



One
Ohm
= The resistance of a
column of mercury (At the
temperature of melting ice) of a
uniform cross section of one square
millimeter and a length of 106.30
centimeters. 
One Volt
= The electromotive force
which produces a current of one
ampere when steadily applied to a
conductor the resistance of which is
one Ohm. 
One
Ampere
= The current which when
passed through a solution of nitrate
of silver in water in accordance
with certain specifications,
deposits silver at the rate of
0.001118+ of a gram per second. 
One
Watt
= The power expended by a
current of one Ampere in a
resistance of one Ohm. 
One
Coulomb = The
quantity of electricity transferred
by a current of one Ampere in one
second. 
One
Farad
= The capacity of a
condenser in which a potential
difference of one volt causes it to
have a charge of one Coulomb of
electricity. 
One Henry
= The inductance in a
circuit in which the electromotive
force induced is one volt when the
inducing current varies at the rate
of one Ampere per second. 
One Joule
= The energy expended in
one second by a flow of one Ampere
in one Ohm. 
The
GramCalorie is the
energy required to raise one gram of
water one degree centigrade in
temperature. One gram calorie
is very nearly equal to 4.18 Joules. 
The
AmpereHour is the
quantity of electricity transferred
by a current of one ampere in
one hour, and is therefore equal to
3600 Coulombs. 
The
Circular
Mil is the unit of
crosssection used in the American
Wire Gauge. The term "Mil"
means one thousandth of an inch
(0.001 inch). It is the area
of a circular wire having a diameter
of one Mil. 
The
Square
Mil is the area of a
square each side of which is one Mil
(0.001 inch). The area of a
square Mil is 0.000001 square
inches. 
The
Circular
MilFoot is a unit
circular conductor one foot in
length and one Mil in diameter.
The resistance of such a unit of
copper has been found experimentally
to be 10.37 ohms at 20 degrees
Celsius. 
The BTU
or British Thermal Unit is
a unit of heat energy and is defined
as the amount of heat necessary to
raise the temperature of one pound
of water one degree Fahrenheit. 
The
Horsepower is equal
to 746 Watts. 



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I
= Current in Amperes 
E
= Volts 
R
= Resistance in Ohms 
P
or
W
= power in Watts 
KW
= Power in Kilowatts 
1KW
= 1,000 watts 
VA
= Apparent Power in
VoltAmperes 
KVA
= apparent power in
KilovoltAmperes 
HP
= Output Power in number of
Horsepower. One
horsepower equals 746 watts 
EFF
= Efficiency, expressed in a
decimal fraction (output
divided by input) 
PF
= Power Factor expressed in
a decimal fraction, the
ratio of true power (P, W,
or KW) divided by apparent
power (VA or KVA) 






Formulae
for SinglePhase AC circuits 

I
= VA ÷ E
Amps equals voltamperes,
divided by volts 
I
= 1,000 x KVA ÷ E
Amps equals one thousand,
times kilovoltamperes,
divided by volts 
I
= W ÷ E x PF
Amps equals watts, divided
by volts, times power factor 
I
= 1,000 x KW ÷ E x PF
Amps equals one thousand,
times kilowatts, divided by
volts, times power factor 
I
= 746 x HP ÷ E x PF x
EFF
Amps equals 746, times
horsepower, divided by
volts, times power factor,
times efficiency 

P
= E x I x PF
Power equals volts, times
amps, times power factor 
VA
= I x E
Voltamperes equals amps,
times volts 
KW
= E x I x PF ÷ 1,000
Kilowatts equals volts,
times amps, times power
factor, divided by 1000 
KVA
= I x E ÷ 1,000
Kilovoltamperes equals
amps, times volts, divided
by 1000 
HP
= I x E x PF x EFF ÷
746
Horsepower equals amps,
times volts, times power
factor, times efficiency,
divided by 746 
Page
Top 






P
= Watts
E
= Volts
I
= Amps
R
= Ohms












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Updated December 13, 2015


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