HesapHanem

Motor Full-Load Current Calculator

Enter motor power, voltage and ratings to find full-load current.

How it is calculated

The tool converts the shaft (output) power into the current drawn from the supply. Three-phase: I = P ÷ (√3 × V × PF × η). Single-phase: I = P ÷ (V × PF × η). Here P is the rated output in watts (you type kilowatts and it multiplies by 1000, so horsepower must be converted first), V is the line voltage in volts, PF is the power factor as a decimal between 0 and 1, and η is efficiency typed as a percent, for example 90, not 0.9. It also reports the apparent input power in kVA, √3 × V × I ÷ 1000 (or V × I ÷ 1000 for single phase). A power factor above 1, or any zero or negative value, gives no result.

Worked example

A three-phase 7.5 kW motor runs on 400 V with a power factor of 0.85 and an efficiency of 90%. Step 1: P = 7.5 × 1000 = 7500 W. Step 2: the denominator is √3 × 400 × 0.85 × 0.90 = 530.0. Step 3: 7500 ÷ 530.0 = 14.15 A. Apparent power is √3 × 400 × 14.15 ÷ 1000 = 9.80 kVA. The same motor on a single-phase supply would draw 24.51 A.

Try this example →

Common mistakes

  • Typing efficiency as 0.9 instead of 90. The tool divides by 100, so 0.9 would be read as 0.9% and the current would come out about 100 times too high.
  • Entering the power in horsepower. The field is in kW, so 10 hp must first be converted to about 7.5 kW.
  • Entering the phase-to-neutral voltage (230 V) for a three-phase motor. The formula expects the line-to-line voltage, for example 400 V.
  • Treating the result as a safe breaker or cable rating. It is the nominal running current, and protection and cable sizing add margins and follow local code.

About this calculator

Full-load current (FLC) is the current an AC motor draws when delivering its rated horsepower at rated voltage — the number stamped on the nameplate and used to size breakers, overload relays, and conductor gauge. This calculator derives it from the motor's power, voltage, power factor, and efficiency rather than reading it off a lookup table.

For a single-phase motor, I = P / (V × PF × η); for three-phase, I = P / (√3 × V × PF × η), where P is output power in watts, V is line voltage, PF is power factor, and η is efficiency (motor input power is always higher than its mechanical output). The √3 factor accounts for the phase relationship between the three line currents in a balanced three-phase system.

Electricians and electrical engineers use full-load current to select the correct wire ampacity per NEC/IEC tables, set thermal overload protection at roughly 115–125% of FLC, and confirm a motor won't nuisance-trip a breaker sized too close to its running current.

Was this helpful?

You can pick up to 3 reactions.

Comments (1)

  • Editorial team

    Compare the result with the motor's nameplate before trusting it. For 15 kW at 400 V, a power factor of 0.85 and 90% efficiency the tool gives 28.30 A, but dropping to 0.70 and 85% raises it to 36.39 A. A nameplate reading well above your calculated figure usually means the real power factor or efficiency is lower than you assumed. Which values do your motors' plates actually list: efficiency, power factor, or both?

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators