How calculate ampere for electric motor?

Generally for electric motor size,it rated by horsepower (hp) or kilowatts (kW) unit.We can recognize the electric motor size when refer to their kilowatts or horsepower.So from power (kW/hp), how we can know the full load ampere for electric motor?

This time i want share about how to calculated the full load ampere (FLA) of electric motor from their power rated.It not difficult if we know the right formula to get the answer.From this calculation we only can estimate the value of full load ampere.

We cannot get the actual full load ampere because it depend on efficiency of motor.If electric motors have a higher efficiency rating,it will draw fewer amps, for example a 10 HP motor with a 60% efficiency rating will draw about 65 amps at 230 VAC compared to about 45 amps for a motor with a 80% rating.


How to calculate from power ( kW & HP ) to ampere ( I )?

1) Kilo watt (kW) to ampere ( I )

For 3 phase power supply ; kW = I x V x 1.732 x pf

For 1 phase power supply ; kW = I x V  x pf

Example : 1 unit compressor size rated 37 kw,415 VAC,3 phase and 80% pf,calculate the full load ampere?

Calculation :

kW = I x V x 1.732 x pf

I = kW / (V x 1.732 x pf )

I = 37 / (415 x 1.732 x 0.8 )

I = (37 / 575) x 1000

I = 64.4 ampere ( full load ampere)


2) Horse power ( hp ) to ampere ( I )

First we must convert from hp to kW using this formula :

1 Hp = 0.746 kW

After that use the formula kW to ampere :

For 3 phase power supply ; kW = I x V x 1.732 x pf

For 1 phase power supply ; kW = I x V x pf


Example :-

1 unit induction motor power rated 25 hp,200 VAC,3 phase,90 % power factor,calculated the full load ampere.

Calculation :-

kW = 25 hp x 0.746

kW = 18.65

kW = I x V x 1.732 x pf

I = kW / V x 1.732 x pf

I = 18.65 / ( 200 x 1.732 x 0.9 )

I = (18.65 / 311.76) x 1000

I = 59.8 ampere ( full load ampere )


  1. Should we take into consideration the efficiency of the motor?.

  2. Steve Sedgwick says

    In your formula Efficiency factor is not accounted – is there some reason for this. I thought the formula was kW = I x V x 1.732 x pf x Efficiency?

  3. Hi. May I help you to calculate the electrical load list of power plan.

  4. Ronald says

    Hi! Is the power factor required also? or If I didn’t know the p.f. can I use 0.8? Our motor specs are 18.5KW, 460V, 3PH.

  5. Akash rajhuns says


    you can also use

    KW = √3 × V× I × cos¢

    cos¢ = 0.8

  6. dheeraj says

    a motors rating 10kw !!!!! what its means this motor will consume 10 kw per sec ??? or 10 kw per hr?????

  7. how did you come about the 1000?please assist


    how can i found 3 ph motor efficiency

  9. Joshy.G.S says

    You should say P = √3VIcos¢
    Watt is the unit of power, to convert Watt to kilo watt divide by 1000
    Then no confusion about 1000

  10. a 48v dc motor with nominal power 11kw. how can i calculate pf

  11. NIRMAL MEHTA says

    440 V, 60 H.P., 55 AMPS, PF .95 & 12 HOURS

    • tukaram haldankar goa says

      60 multiply by 0.746 as converting ratio you will get watts per hour and multiple for 12 hour is 44.760 kilowatts per hour multiple for 12 hour is 537.12 for 12 hour, calculate this kw multiple ain unit charges by electricity per unit you will get your bill……

  12. M.NARESH says

    1 HP = .746 KW

    20 HP = 20 * 0.746
    = 14.92 KW

    P = √3 V I cos¢
    P = 14.92 KW
    V = 415 V
    cos¢ = 0.8
    √3 = 1.732
    I = ????

    P = √3 V I cos¢
    I = ( P / √3 V cos¢ )
    I = (( 14.92*1000 ) / ( 1.732 * 415 * 0.8 ))
    I = 25.94 A
    I = 26 A

  13. M.NARESH says


  14. I made a blower. The fan is OD 33.5″
    6″thickness and 55 kg Wight
    Which power motor required (HP)

  15. I made a blower. The fan is OD 33.5″
    6″thickness and 55 kg Wight
    Which power motor required (HP)
    2800 rpm

  16. tushar says

    hiee, for 3 phase 1kw ac motor how much the maximum current rating is acceptable?

  17. Littu chirayil says

    How to calculate amper when horsepower is given for 3 phase ?

  18. himanshu says

    A 20 H.P, 3 Phase supply ,50Hz , 440 Volt in induction motor .find out full load current?

  19. we are having 3-phase BLDC hub motor (800W ,48V).
    we have to run this motor for 2 hours with Lithium-ion battery.
    Then how to decide the battery capacity?

  20. Narsing says

    how to find pf

  21. Is motor rpm is necessary to calcultae full load current?

  22. MEshari says

    how to Calculate the actual running current of a motor such as: moter name plate:
    incoming V=480V using softstarter

  23. sushil says

    which type (watt) inverter require for run 1 hp electric motor.
    pls given best answer .

  24. Hi Gents
    I have a pump with Diesel engine 1450 RPM, 160 KW, Soi wants to change the diesel engine by Electrical Motor 1450 RPM, 160 KW, 3 Ph, 380 Volts, 50 Hz, so I need to know how many Amp. I need for each one phase ( they write in the motor 280 Amp is this total for all 3 ph or 280 Amp for each one phase ) Cheers….

  25. Hi, if I’m having 15 kW motor , 3phase, pf .8 star-delta starter. How can I find How much current will flow in star condition & how much in Delta?! Pls answer. Thank you

  26. Starting current of 10 HP induction Motor is_________ times full load current

    • John Lemau says

      It depend what motor starter that you use..

      DOL –> 5- 6 X FLA
      AUTO TRANS –> 3-4 X FLA
      STAR DELTA –> 3-4 X FLA

      The best is VFD – Variable Frequency Drive

  27. We have motor rating in KW, it means KW power take in how much time

  28. karthi says

    what is the current rating of 200hp motor?

  29. Jitendra Lohar says

    1. How to calculate stating current of single phase and three phase motor ?
    2. How to decide or calculate start capacitor or running capacitor for single phase motor ?

  30. inayat Hussain says

    A motor follows the operation as
    Load duty cycle
    20kW 120 sec
    10kW 120 sec
    Stopped 280 sec

    What will be the continuous rating of motor for above operation.

  31. Ashish Patidar says

    I have 2 same motor (equal power, rating and brand) 3 Phase, running on same type of job on two different machines, one of them is drawing 45 amps where as other is drawing 50 amps of current. They run 24*7 in plant so i want know is how much unit each one consuming ??

  32. NIRMAL says


  33. Good way of explaining, and pleasant post to take facts regarding my presentation subject matter,
    which i am going to convey in college.

  34. i have a dout please help me
    when 3 phase supply input it will be rectified ,so the rectified dc power 10kw ,then it will be through on filter so how i can choose the capacitor value and i want proper calculation
    in the circuit dc voltage?
    filter capacitor value?
    capacitor ripple peak current and peak voltage?
    any one can solve the problem please reply

  35. 0.37 kw motor Thermal overload setted 1.1 amps
    400v 3ph ac 50 hz

    motor data
    No load current 0.67 amps
    Full load amps 1.09 amps
    pls explain anybody
    what concept on this

  36. What will be the motor load in 3 phase 40 hpmotor runs ons 960 rpm ??

  37. what is the full load amp in given details below..?
    1hp motor ,240v rating ?
    Please share the ans and detail calculation with pf ?

  38. What could the maximum current and rated current for a motor with following specs:-
    3 phase
    415 V
    11 kW

  39. Prahlad Choudhary says

    Sir normally 25hp 3phase motor 440volt. Per kitne amp’s current khapt karta h

  40. Fadhili Issa says

    Hello. Am a big fan of your precise guidance on this matter.
    Please assist me on the calculation of the amperage by considering the Service Factor of the motor.

    • John Lemau says

      Service factor is the percentage multiplier that a motor can handle for short periods of time when operating within its normal voltage and frequency tolerance.SF is intended for unpredictable and brief overload conditions, not for continuous operation or intentional short-term overload.

      example :
      SF 1.15 = 15% more from motor HP/kW
      5HP = 3700Watts
      SF = 1.15 = 15%
      3700 + 15% = 4255W
      So the motor will be loaded to 4255W and current consumed in that load is declared as SFA.

  41. Mahendra says

    240 hp
    292 amp
    180 kw
    415 volt
    3 phase induction motor
    I now that par phase amp

  42. aju. A says

    a 3 phase 15 hp. motor so plz find full load ampere

  43. Narottam sahoo says

    A 5hp,400v ,3phase motor having 75%efficiency and operating at pf of 0.8 takes a current of ——–A

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