Motor HP to Amps Calculator

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Calculate estimated motor full-load amps from horsepower, voltage, phase, efficiency and power factor, then compare common 1 HP, 5 HP, 7.5 HP, 10 HP and larger three-phase current chart values.

Inputs

Motor output rating (HP)

Supply

Supply voltage (V)

Use line-to-line voltage for three phase.

Motor efficiency (%)

Power factor

Starting-current multiple (× FLC)

Use the motor datasheet or starter study where available.

How to use this calculator: Motor HP to Amps Calculator

Calculate estimated motor full-load amps from horsepower, voltage, phase, efficiency and power factor, then compare common 1 HP, 5 HP, 7.5 HP, 10 HP and larger three-phase current chart values. The example below is calculated by this page's real engine from the displayed inputs.

1Use the rated shaft-output HP from the motor nameplate, not the connected mechanical load estimate.
2Select single or three phase and enter the actual RMS supply voltage. Use line-to-line voltage for three phase.
3Replace the defaults with the motor's efficiency and power factor. Small and lightly loaded motors can differ substantially.
4Use the calculated running current for an estimate and the starting-current result for starter and voltage-dip screening.
5Before selecting cable, breaker, overload or contactor, check the nameplate, manufacturer curves and the relevant IEC/NEC rules.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

Input	Example value	Why it matters
Motor output rating	5 HP	Measured or known motor output rating used by the calculation engine.
Supply	Three phase	Select the option that matches the real installation or scenario.
Supply voltage	415 V	Use line-to-line voltage for three phase.
Motor efficiency	90 %	Measured or known motor efficiency used by the calculation engine.
Power factor	0.85	Measured or known power factor used by the calculation engine.
Starting-current multiple	6 × FLC	Use the motor datasheet or starter study where available.

Formula, derivation and worked example

Horsepower is mechanical output power, while the electrical supply must also cover motor losses and reactive current. The calculator first converts HP to watts, divides by efficiency to get input power, then applies the correct single-phase or three-phase current equation. It is an engineering estimate; the motor nameplate and the applicable code table govern final conductor and protection selection.

Pout = HP × 746 W

Pin = Pout / efficiency

Single phase: I = Pin / (V × PF)

Three phase: I = Pin / (√3 × VLL × PF)

Estimated starting current = full-load current × starting multiple

Substitution steps

1. Mechanical output
HP × 746
= 3,730 W
2. Electrical input
Pout / efficiency
= 4,144 W
3. Running current
Pin / (√3 × VLL × PF)
= 6.78 A
4. Starting current
I × starting multiple
= 40.7 A

Computed example results

Estimated full-load current: 6.78 A; Three-phase equation
Motor output: 3.73 kW
Electrical input: 4.144 kW; at 90% efficiency
Estimated starting current: 40.7 A; 6 × full-load current
125% continuous-duty reference: 8.48 A; screening value; apply the governing motor-circuit rule
Apparent input power: 4.876 kVA

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using Motor HP to Amps Calculator

Do not mix units for Motor output rating (HP), Supply voltage (V), Motor efficiency (%). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
Do not leave Supply on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
Do not replace the displayed Pout = HP × 746 W relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
Do not treat Estimated full-load current = 6.78 A from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

Next logical calculator

Continue with kVA, kW and Amps Calculator

Useful next check because both tools use Supply voltage and Power factor, while kVA, kW and Amps Calculator answers a different part of the same workflow.

Open kVA, kW and Amps Calculator

Standards, source trail and limitations

References show the method used. Check the current local edition, amendments and project specification before a regulated decision.

HP to amps formula for single-phase and three-phase motors

Motor horsepower is mechanical shaft output, so HP cannot be converted to amps from voltage alone. The electrical input must also account for efficiency and power factor. For three phase, estimated full-load current is HP × 746 ÷ (√3 × line voltage × efficiency × power factor). For single phase, remove the √3 term.

The live calculator lets you replace the default efficiency and power factor with the motor nameplate values. That is more accurate than using a generic HP chart, especially for small motors, premium-efficiency motors and motors operating away from rated load.

1 HP, 5 HP and 7.5 HP motor amps at 415 V three phase

Using the chart assumption of 90% efficiency and 0.85 power factor, a 1 HP motor is about 1.36 A at 415 V three phase, 5 HP is about 6.78 A and 7.5 HP is about 10.17 A. A 10 HP motor is about 13.57 A on the same assumptions.

These are equation-based estimates, not universal motor nameplate currents. Manufacturer design, efficiency class, power factor, voltage tolerance and loading can move the actual full-load current, so final cable, overload and protection settings should use the governing data and rules.

Why a three-phase motor draws less current at higher voltage

For the same mechanical output, current is inversely related to supply voltage. That is why the chart shows slightly lower current at 440 V than at 400 V. Three-phase power also includes the √3 relationship between line voltage and line current.

Do not compare a 230 V single-phase current directly with a 415 V three-phase current without accounting for both the different voltage and phase equation.

Running current, starting current and protection are different

The calculated full-load current estimates steady operation near rated load. Induction motors can draw several times that current during starting, depending on motor design and starter method. The starting-current multiple input gives a screening estimate for voltage-dip and starter checks.

Breaker, fuse, overload relay, contactor and cable sizing are not chosen from one current number alone. Follow the motor nameplate, manufacturer data and the applicable IEC or NEC motor-circuit provisions for the final design.

Formula

Pout = HP × 746 W
Pin = Pout / efficiency
Single phase: I = Pin / (V × PF)
Three phase: I = Pin / (√3 × VLL × PF)
Estimated starting current = full-load current × starting multiple

HP to amps motor current chart – common single-phase and 3-phase voltages

Equation-based planning values at 90% efficiency and 0.85 power factor. Actual nameplate current can differ; use manufacturer/nameplate and applicable motor-circuit rules for final design.

Motor HP	Output kW	230 V 1-phase	400 V 3-phase	415 V 3-phase	440 V 3-phase
0.5 HP	0.373 kW	2.12 A	0.7 A	0.68 A	0.64 A
0.75 HP	0.559 kW	3.18 A	1.06 A	1.02 A	0.96 A
1 HP	0.746 kW	4.24 A	1.41 A	1.36 A	1.28 A
1.5 HP	1.119 kW	6.36 A	2.11 A	2.03 A	1.92 A
2 HP	1.492 kW	8.48 A	2.82 A	2.71 A	2.56 A
3 HP	2.238 kW	12.72 A	4.22 A	4.07 A	3.84 A
5 HP	3.73 kW	21.2 A	7.04 A	6.78 A	6.4 A
7.5 HP	5.595 kW	31.8 A	10.56 A	10.17 A	9.6 A
10 HP	7.46 kW	42.4 A	14.08 A	13.57 A	12.8 A
15 HP	11.19 kW	63.6 A	21.11 A	20.35 A	19.19 A
20 HP	14.92 kW	84.8 A	28.15 A	27.13 A	25.59 A
25 HP	18.65 kW	106 A	35.19 A	33.92 A	31.99 A
30 HP	22.38 kW	127.2 A	42.23 A	40.7 A	38.39 A
40 HP	29.84 kW	169.59 A	56.3 A	54.27 A	51.18 A
50 HP	37.3 kW	211.99 A	70.38 A	67.83 A	63.98 A

Formulas explained

I3φ = HP × 746 / (√3 × VLL × η × PF)

The shaft rating is divided by efficiency to recover electrical input power. Three-phase real power is √3 × line voltage × line current × power factor.

HP: Rated mechanical shaft output in horsepower.
η: Motor efficiency as a decimal.
PF: Full-load power factor.
VLL: Line-to-line RMS voltage.

Actual current changes with load, voltage, design class and motor construction; use the nameplate when available.

1 HP at 415 V three phase

About 1.36 A using 90% efficiency and 0.85 PF. Use the motor nameplate full-load current for final design.

5 HP at 415 V three phase

About 6.78 A on the same equation assumptions. Estimated DOL starting current at 6× would be about 40.7 A.

7.5 HP at 415 V three phase

About 10.17 A at 90% efficiency and 0.85 PF. Actual current varies with the specific motor.

Worked example

15 HP, 415 V three phase, efficiency 90%, power factor 0.85.
2Output = 5 × 746 = 3,730 W; input = 3,730 / 0.90 = 4,144 W.
3Current = 4,144 / (1.732 × 415 × 0.85) = 6.78 A; estimated 6× starting current = 40.7 A.

Assumptions

Balanced supply at rated voltage.
Efficiency and power factor apply at the entered operating point.

Warnings

Do not select overload protection from the calculated value when a readable nameplate current is available.
Starting-current multiples vary with motor design and starter method.

Standards & references

IEC 60034-1
IEC 60364-5-52
NFPA 70 (NEC) Article 430

Frequently asked questions

How many amps does a 5 HP three-phase motor draw?

At 415 V, 90% efficiency and 0.85 PF, the equation gives about 6.8 A. Use the nameplate current for final protection and cable selection.

Why is motor current higher than HP × 746 divided by voltage?

Because the supply also covers motor losses and reactive current. Efficiency and power factor both increase the input current.

Is starting current the same as full-load current?

No. Direct-on-line induction motors can briefly draw several times full-load current. The exact multiple depends on motor design and starting method.

Can this result choose my breaker?

It is a screening value only. Breaker, overload and cable selection must follow the motor nameplate, starting method and the applicable code.

How many amps is a 1 HP motor at 415 V three phase?

About 1.36 A using 90% efficiency and 0.85 power factor. The actual motor nameplate current can differ.

How many amps is a 5 HP motor at 415 V three phase?

About 6.78 A at 90% efficiency and 0.85 PF. Use the live calculator with the motor's real efficiency and PF for a better estimate.

How many amps is a 7.5 HP motor at 415 V three phase?

About 10.17 A using the chart assumptions of 90% efficiency and 0.85 power factor.

How many amps is a 10 HP motor at 415 V three phase?

About 13.57 A on the same assumptions. Nameplate current remains the preferred value for final cable and protection selection.

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