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Electrical Power CalculatorsThe 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
Power Calculator
Converting kVA to kW
Converting kW to kVA
Converting kW to HP
Amperes when kVA is known
kVA Required to run motors
Guide to Standard Uints
Kilo Volt Amperes kVA
KiloWatts (1000 watts = 1 kW)
kW
Ampere (Volt-Amperes or Current)
I
Volts E
Power Factor PE
Percent Efficiency %EFF
Horse Power HP
Power Requirement Calculator
PhaseVolts
RequiredV
AmperesI
PowerFactor = Power
kW
1
3
.8
1.0
Converting kW to kVA
kW=
kVA
Converting kVA to kW
kVA=kW
Converting kW to HP
kW=HP
What size genset is needed to start a 3 phase electric motor Direct on Line (DOL) start
HP ofMotor =
GeneratorkVA Required
Calculating Amperes
(when you know kVA)
Phase
1,2,3
GeneratorkVA
VoltsRequired
=
AmpereI
Standard Electrical Formulas Used for Power Consumption Calculations
TO DETERMINE: SINGLE-PHASE THREE-PHASEDIRECT
CURRENT
KVAI x E1000
I x E x 1.731000
--------
Kilowatts I x E x PF1000
I x E x 1.73 x PF1000
I x E1000
HorsepowerI x E x %EFF x PF
746I x E x 1.732 x %EFF x PF
746I x E x %EFF
746
Amperes (when HP is known) HP x 746 E x %EFF x PF
HP x 746 1.73 x E x %EFF x PF
HP x 746E x %EFF
Amperes (when kW is known)KW x 1000
E x PFKW x 1000
1.73 x E x PFKW x 1000
E
Amperes (when KVA is known)KVA x 1000
EKVA x 1000
1.73 x E
Total Power CalculationThis 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)
Known Variables: Real Power, Reactive Power
Input Three Phase Power (kW)
Input Three Phase Reactive Power (kvar)
Calculated Total Power (kva)
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)
• 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
Fundamentals: Electric Laws − Formulary − Equations
Formula wheel ▼ Important formulasElectrical 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 × I2 = 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
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
Power factor PF = cos φ = R/(R2 + X2)1/2, 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 URN 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 UP = 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