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Electrical Power Calculators The following calculators are provided to help you determine the size of generator required foryour specific application. Other calculators on this page are for unit conversions and other powerrelated calculations.

Calculation

Power Calculator

Converting kVA to kW

Converting kW to kVA

Converting kW to HP

Amperes when kVA isknown

kVA Required to runmotors

Guide to StandardUints

Kilo Volt Amperes kVA

KiloWatts (1000watts = 1 kW)

kW

Ampere (Volt-Amperes orCurrent)

I

Volts E

Power Factor PE

Percent Efficiency %EFF

Horse Power HP

 

Power Requirement Calculator

Phase

VoltsRequire

dV

AmperesI

PowerFactor =

PowerkW

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 isneeded to start a 3 phaseelectric motor Direct onLine (DOL) start

HP of  

Motor =

GeneratorkVA

Required

Calculating Amperes (when you knowkVA)

Phase

Generator

VoltsRequire

= AmpereI

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1,2,3 kVA d

Standard Electrical Formulas Used for Power Consumption Calculations

TO DETERMINE: SINGLE-PHASE THREE-PHASEDIRECT

CURRENT

KVAI x E1000

I x E x 1.731000

--------

KilowattsI x E x PF

1000I x E x 1.73 x PF

1000I x E1000

Horsepower I x E x %EFF x PF746 I x E x 1.732 x %EFF x PF746 I x E x %EFF746

Amperes (when HP is known)HP x 746

E x %EFF x PFHP x 746

1.73 x E x %EFF x PFHP 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 Calculation

This web page can be used to calculate the total power (kva) of a single phase or three phase load. Use Tableone for three phase calculations, and use Table two for single phase calculations. The three phase loadcalculations 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  

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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 ElectricCharge

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.

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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 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 FormulasElectrical and mechanical power calculation

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Formula 1 − Electrical (electric) power equation: Power   P = I × V =

 R × I 2 = V 2   ∕   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 notdo neither the intensity, nor the power or the energy. If you are in the

audio recordingbusiness, it is therefore wise not to care much about the energy,

power and intensity.

Very loud sounding speakers should have much power, but lookcloser at the veryimportant 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 acalculation 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 inwatts 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 whendemanding higher power.

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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 thecalculation.

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Please enter two values, the third value will be calculated.

Electric Power P: watts

Voltage V : voltsAmperage I : amps

reset

Calculations: Ohm's law - Ohm'smagic triangle

ALTERNATING CURRENT (AC) ~

V l = line voltage (volts), V p = phase voltage (volts), I l = line current (amps), I p = phase current (amps)

 Z = impedance (ohms), P = power (watts), φ = power factor angle, VAR = volt-amperes (reactive)

Current (single phase): I = P / V p×cos φ Current (3 phases): I = P / 3 √ V l×cos φ or I = P / 3 V p×cos φ 

Power (single phase): P = V p× I p×cos φ Power (3 phases): P = 3 √ V l× I l×cos φ or P = 3 √ V p× I p×cos φ 

Power factor PF = cos φ = R/(R2 + X2)1/2, φ = power factor angle. For the purely resistive circuit, PF = 1

(perfect).

 

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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 phasesequence 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 phasevoltage)

 

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 isbalanced, the current in the neutral is zero and the total power is

 

P = 3UL IL cosØ  

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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 asreference.

The voltage applied to any load is the line voltage UL and the line current is the phasor differencebetween the currents in the two loads connected to that line. If the load currents are all equal and makeequal phase angles with their respective voltages the system is balanced and

 

IL = 3IP  

The total power under these conditions is  

P = 3UL IL cosØ