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