Electrical Power Calculators
The following calculators are provided to help you determine the size of generator required for your specific
application. Other calculators on this page are for unit conversions and other power related calculations.
Calculation Guide to Standard Uints
Power Calculator Kilo Volt Amperes kVA
Converting kVA to kW KiloWatts (1000 watts
kW
= 1 kW)
Converting kW to kVA
Ampere (Volt-
I
Converting kW to HP Amperes or Current)
Amperes when kVA is known Volts E
kVA Required to run motors Power Factor PE
Percent Efficiency %EFF
Horse Power HP
Power Requirement Calculator
Volts
Amperes Power Power
Phase Required
I Factor = kW
V
1 380 240 .8
3 1.0
Converting Converting
kW to kVA kVA to kW
k k
k k
W =
V V =
W
A A
480 600
What size genset is needed to
Converting
start a 3 phase electric motor
kW to HP
Direct on Line (DOL) start
k H
W=
HP of Generator
P
Motor = kVA Required
50
85
Calculating Amperes (when
you know kVA)
P G V
=A
h
e ol
a
n ts
s m
er R
e p
at e
1 er
or q
, e
k ui
2 I
V re
,
A d
3
1 500240
Standard Electrical Formulas Used for Power
Consumption Calculations
DIRECT
TO DETERMINE: SINGLE-PHASE THREE-PHASE
CURRENT
IxE I x E x 1.73
KVA --------
1000 1000
I x E x PF I x E x 1.73 x PF IxE
Kilowatts 1000 1000 1000
I x E x %EFF x PF I x E x 1.732 x %EFF x PF I x E x %EFF
Horsepower
746 746 746
HP x 746 HP x 746 HP x 746
Amperes (when HP is known)
E x %EFF x PF 1.73 x E x %EFF x PF E x %EFF
KW x 1000 KW x 1000 KW x 1000
Amperes (when kW is known)
E x PF 1.73 x E x PF E
KVA x 1000 KVA x 1000
Amperes (when KVA is known)
E 1.73 x E
Total Power Calculation
This web page can be used to calculate the total power (kva) of a single phase or three phase load. Use Table
one for three phase calculations, and use Table two for single phase calculations. The three phase load
calculations assume the load is balanced.
Table 1 - Calculation of Total Power Three Phase Loads
Known Variables: Voltage, Current
Input System Line-Line Voltage (kv)
Input line current (amps)
Calculated Total Power (kva)
Compute
Known Variables: Real Power, Reactive Power
Input Three Phase Power (kW)
Input Three Phase Reactive Power (kvar)
Calculated Total Power (kva)
Compute
Table 2 - Calculation of Total Power Single Phase Loads
Known Variables: Voltage, Current
Input System Line to Neutral Voltage (kv)
Input Line Current (amps)
Calculated Total power (kva)
Compute
• Formulas and calculations •
The relationship between
Electrical voltage V, amperage I, resistivity R, impedance Z,
wattage P
Electricity and Electric
Charge
The nominal impedance Z = 4, 8, and 16 ohms (loudspeakers) is often assumed as resistance R.
Ohm's law equation (formula): V = I × R and the power law equation (formula): P = I × V.
P = power, I or J = Latin: influare, international ampere, or intensity and R = resistance.
V = voltage, electric potential difference or E = electro motive force (EMF = voltage).
Enter any two of the following values and click the calculation button.
The missing values will be calculated. Enter only two values.
The used Browser unfortunately supports no Javascript.
The program is indicated, but the actual function is missing.
Voltage or volt E or V = volts V
Amperage or current I = amperes, amps A
Resistivity or resistance R = ohms Ω
Wattage or power P = watts W
For R take impedance Z reset
Fundamentals: Electric Laws − Formulary − Equations
Formula wheel ▼ Important formulas
Electrical engineering laws Electronic engineering laws
V comes from "voltage" and E from "electromotive force". E means also energy,
so V is chosen.
The Big Power Formulas
Electrical and mechanical power calculation
Formula 1 − Electrical (electric) power equation: Power P = I × V =
R × I 2 = V2 ⁄ R
where power P is in watts, voltage V is in volts and current I is in
amperes (DC).
If there is AC, look also at the power factor PF = cos φ and φ =
power factor angle
(phase angle) between voltage and amperage.
Formula 2 − Mechanical (mechanic) power equation: Power P = E ⁄
t=W⁄t
where power P is in watts, Energy E is in joules, and time t is in
seconds. 1 W = 1 J/s.
Power = force times displacement divided by time P = F · s / t or:
Power = force times speed (velocity) P = F · v.
Electric (electrical) Energy is E = P × t − measured in watthours, or
also in kWh.
Undistorted powerful sound is not to find in these formulas. Please,
mind your ears!
The eardrums are really only moved by the waves of the sound
pressure. That does not
do neither the intensity, nor the power or the energy. If you are in the
audio recording
business, it is therefore wise not to care much about the energy,
power and intensity.
Very loud sounding speakers should have much power, but look
closer at the very
important efficiency of loudspeakers. This includes the typical
question:
How many decibels (dB) are actually twice or three times as
loud?
There is really no RMS power. The words "RMS power" show not
correct, that there is a
calculation of a power which is the multiplication of a voltage RMS
and an amperage RMS.
RMS watts is meaningless. In fact, we use that term as an extreme
shorthand for power in
watts calculated from measuring the RMS voltage. Please, read
here:
Why there is no such thing as 'RMS watts' or 'watts RMS' and
never has been.
Power is the amount of energy that is converted in a unit of time.
Expect to pay more when
demanding higher power.
Tip: The electrical power triangle (power formula)
The magic triangle can be used to calculate all formulas of the "electric power
law". You hide with
a finger the value to be calculated. The other two values show then how to do the
calculation.
Please enter two values, the third value will be calculated.
Electric Power P: watts
Voltage V: volts
Amperage I: amps
reset
Calculations: Ohm's law - Ohm's
magic triangle
ALTERNATING CURRENT (AC) ~
Vl = line voltage (volts), Vp = phase voltage (volts), Il = line current (amps), Ip = phase current (amps)
Z = impedance (ohms), P = power (watts), φ = power factor angle, VAR = volt-amperes (reactive)
Current (single phase): I = P / Vp×cos φ Current (3 phases): I = P / √3 Vl×cos φ or I = P / 3 Vp×cos φ
Power (single phase): P = Vp×Ip×cos φ Power (3 phases): P = √3 Vl×Il×cos φ or P = √3 Vp×Ip×cos φ
1/2
Power factor PF = cos φ = R/(R2 + X2) , φ = power factor angle. For the purely resistive circuit, PF = 1
(perfect).
3 Phase Circuit Calculations
Star Connection
Figure 1 Figure 2
Figure 1 shows three loads connected in the star formation to a three phase four wire supply
system. Figure 2 shows the phasor diagram, the red to neutral voltage U RN is taken as
reference and the phase sequence is red, yellow, blue so that the other line to neutral voltages
or phase voltages lie as shown.
If URN = UYN = UBN and they are equally spaced the system of voltage is balanced.
Let UL be the voltage between any pair of lines (the line voltage) and U P = URN = UYN = UBN
(the phase voltage)
Then UL = 3UP
and IL = IP
where IL is the current in any line and IP is the current in any load or phase. The power per
phase is P = UPIPcosØ and the total power is the sum of the amount of power in each phase
If the currents are equal and the phase angles are the same as in figure 3 the load on the
system is balanced, the current in the neutral is zero and the total power is
P = 3UL IL cosØ
Figure 3
Delta Connections
Figure 4 Figure 5
Figure 4 shows three loads connected in the delta or mesh formation to a three phase supply
system. Figure 5 shows the phasor diagram of the line voltages with the red to yellow voltage
taken as reference.
The voltage applied to any load is the line voltage UL and the line current is the phasor
difference between the currents in the two loads connected to that line. If the load currents are
all equal and make equal phase angles with their respective voltages the system is balanced
and
IL = 3IP
The total power under these conditions is
P= 3UL IL cosØ
