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Amps to HP Calculator

Convert electrical current in amperes (A) to mechanical power in horsepower (HP) for DC, single-phase AC, and three-phase AC motors.

Calculate HP from Amps

Circuit Type

Current (Amps)

Voltage (V)

Motor Efficiency (0-1)

Power Factor (0-1)

Amps to HP Formulas

DC Motors

HP = (V × A × Eff) ÷ 746

Single-Phase AC

HP = (V × A × Eff × PF) ÷ 746

Three-Phase AC

HP = (√3 × V × A × Eff × PF) ÷ 746

What Is Amps to Horsepower Conversion?

Converting amperes (amps) to horsepower (HP) bridges the gap between electrical measurement and mechanical power output, essential for electric motor applications. The conversion depends on voltage, efficiency, and power factor. For DC motors: HP = (V × I × Efficiency) ÷ 746. For AC motors: HP = (V × I × PF × Efficiency) ÷ 746 (single-phase) or HP = (V × I × PF × Efficiency × 1.732) ÷ 746 (three-phase). One mechanical horsepower equals 746 watts. This conversion is fundamental in motor selection, circuit breaker sizing, and industrial automation design per NEC Article 430.

How to Calculate Amps to Horsepower Conversion

1
Select Motor Type
Choose between DC motor, single-phase AC motor, or three-phase AC motor. This determines which formula the calculator uses and what additional parameters are needed.
2
Enter Current in Amps
Input the measured or rated current draw of the motor. Use a clamp meter for existing installations or refer to the motor nameplate for rated full-load amps (FLA).
3
Enter Voltage
Input the supply voltage. Common motor voltages: 120V/240V (residential single-phase), 208V/480V (commercial three-phase), 12V/24V/48V (DC motors).
4
Set Efficiency and Power Factor
Enter motor efficiency (typically 80-95% for modern motors) and power factor (0.80-0.90 for induction motors). These values are found on the motor nameplate or manufacturer datasheet.

Why Amps to Horsepower Conversion Matters

Motor Selection and Sizing

Properly converting amps to HP ensures you select the right motor for your application. Undersized motors overheat and fail prematurely; oversized motors waste energy and cost more upfront.

Circuit Protection Per NEC 430

The National Electrical Code requires circuit breakers and wire sizing based on motor HP and full-load amps. Accurate amps-to-HP conversion ensures code-compliant electrical installations.

Energy Efficiency Auditing

Comparing measured amps to rated HP reveals motor loading. A motor drawing significantly fewer amps than expected may be oversized, wasting energy through lower efficiency at partial loads.

Variable Frequency Drive Sizing

VFD selection requires knowing both HP and full-load amps. Converting between these values ensures proper VFD sizing for motor speed control applications in HVAC and manufacturing.

Electrical Safety Tips & Best Practices

Use Nameplate Data First

Motor nameplates provide rated HP, voltage, FLA, service factor, and efficiency. Use nameplate values rather than calculated values for NEC compliance and equipment sizing.

Account for Motor Service Factor

Motors with a 1.15 service factor can continuously operate at 115% of rated HP. However, running at service factor increases heat and reduces motor lifespan. Size circuits for service factor amps.

Locked Rotor Amps Are Higher

Starting current (locked rotor amps) is 5-8 times higher than running amps. Circuit breakers and starters must handle inrush current without nuisance tripping.

Three-Phase is More Efficient

Three-phase motors are more efficient and deliver smoother torque than single-phase equivalents. For motors above 5 HP, three-phase is strongly preferred in industrial applications.

Amps to HP Chart (3Φ, Eff=0.9, PF=0.85)

Amps	120V	208V	240V	480V
1 A	0.12 HP	0.21 HP	0.24 HP	0.48 HP
5 A	0.6 HP	1.05 HP	1.2 HP	2.4 HP
10 A	1.2 HP	2.1 HP	2.4 HP	4.8 HP
15 A	1.8 HP	3.15 HP	3.6 HP	7.2 HP
20 A	2.4 HP	4.2 HP	4.8 HP	9.6 HP
30 A	3.6 HP	6.3 HP	7.2 HP	14.4 HP
50 A	6 HP	10.5 HP	12 HP	24 HP
100 A	12 HP	21 HP	24 HP	48 HP

Frequently Asked Questions

How many HP is 10 amps at 240V?

For a three-phase motor with 90% efficiency and 0.85 power factor: HP = (√3 × 240 × 10 × 0.9 × 0.85) ÷ 746 = 4.3 HP approximately.

Why do I need efficiency and power factor?

The current drawn by a motor includes losses and reactive power. Efficiency accounts for mechanical and electrical losses. Power factor accounts for the phase difference between current and voltage in AC motors.

How do I find motor efficiency?

Check the motor nameplate or manufacturer specifications. NEMA Premium efficiency motors typically range from 85-96% depending on size. Standard motors are 2-4% lower.

How many amps does a 1 HP motor draw?

A 1 HP single-phase 120V motor draws approximately 16 amps at full load. At 240V single-phase, it draws about 8 amps. A 1 HP three-phase 208V motor draws about 4.6 amps. These are approximate values — actual current depends on motor efficiency and power factor.

What is the formula for amps to HP?

For DC: HP = (Amps × Volts × Efficiency) ÷ 746. For single-phase AC: HP = (Amps × Volts × Power Factor × Efficiency) ÷ 746. For three-phase AC: HP = (Amps × Volts × 1.732 × Power Factor × Efficiency) ÷ 746.

Why is 746 used in HP calculations?

One mechanical horsepower equals 746 watts. James Watt defined horsepower as 33,000 foot-pounds per minute, which converts to approximately 746 watts. This conversion factor bridges mechanical power (HP) and electrical power (watts) measurements.

What power factor should I use for motors?

Typical power factors for induction motors: small motors (under 1 HP) 0.60-0.75, medium motors (1-10 HP) 0.75-0.85, large motors (over 10 HP) 0.85-0.92. Synchronous motors and motors with power factor correction can reach 0.95-1.0.

How does motor efficiency affect the conversion?

Motor efficiency represents how much electrical power converts to mechanical output. A 90% efficient motor rated at 10 HP actually consumes 10 ÷ 0.90 = 11.1 HP worth of electrical power. NEMA Premium efficiency motors (92-96%) reduce energy waste and operating costs.

References & Industry Standards

NEC Article 430 - Motors, Motor Circuits, and Controllers
NEMA MG 1 - Motors and Generators Standards
IEEE 112 - Standard Test Procedure for Polyphase Induction Motors
IEC 60034 - Rotating Electrical Machines

Last updated: 2026-02-01 | Reviewed by UnitTables Engineering Team

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What Is Amps to Horsepower Conversion?

How to Calculate Amps to Horsepower Conversion

Select Motor Type

Choose between DC motor, single-phase AC motor, or three-phase AC motor. This determines which formula the calculator uses and what additional parameters are needed.

Enter Current in Amps

Input the measured or rated current draw of the motor. Use a clamp meter for existing installations or refer to the motor nameplate for rated full-load amps (FLA).

Enter Voltage

Input the supply voltage. Common motor voltages: 120V/240V (residential single-phase), 208V/480V (commercial three-phase), 12V/24V/48V (DC motors).

Set Efficiency and Power Factor

Enter motor efficiency (typically 80-95% for modern motors) and power factor (0.80-0.90 for induction motors). These values are found on the motor nameplate or manufacturer datasheet.

Why Amps to Horsepower Conversion Matters

Motor Selection and Sizing

Properly converting amps to HP ensures you select the right motor for your application. Undersized motors overheat and fail prematurely; oversized motors waste energy and cost more upfront.

Circuit Protection Per NEC 430

The National Electrical Code requires circuit breakers and wire sizing based on motor HP and full-load amps. Accurate amps-to-HP conversion ensures code-compliant electrical installations.

Energy Efficiency Auditing

Comparing measured amps to rated HP reveals motor loading. A motor drawing significantly fewer amps than expected may be oversized, wasting energy through lower efficiency at partial loads.

Variable Frequency Drive Sizing

VFD selection requires knowing both HP and full-load amps. Converting between these values ensures proper VFD sizing for motor speed control applications in HVAC and manufacturing.

Electrical Safety Tips & Best Practices

Use Nameplate Data First

Motor nameplates provide rated HP, voltage, FLA, service factor, and efficiency. Use nameplate values rather than calculated values for NEC compliance and equipment sizing.

Account for Motor Service Factor

Motors with a 1.15 service factor can continuously operate at 115% of rated HP. However, running at service factor increases heat and reduces motor lifespan. Size circuits for service factor amps.

Locked Rotor Amps Are Higher

Starting current (locked rotor amps) is 5-8 times higher than running amps. Circuit breakers and starters must handle inrush current without nuisance tripping.

Three-Phase is More Efficient

Three-phase motors are more efficient and deliver smoother torque than single-phase equivalents. For motors above 5 HP, three-phase is strongly preferred in industrial applications.

Amps

120V

208V

240V

480V

1 A

0.12 HP

0.21 HP

0.24 HP

0.48 HP

5 A

0.6 HP

1.05 HP

1.2 HP

2.4 HP

10 A

1.2 HP

2.1 HP

2.4 HP

4.8 HP

15 A

1.8 HP

3.15 HP

3.6 HP

7.2 HP

20 A

2.4 HP

4.2 HP

4.8 HP

9.6 HP

30 A

3.6 HP

6.3 HP

7.2 HP

14.4 HP

50 A

6 HP

10.5 HP

12 HP

24 HP

100 A

12 HP

21 HP

24 HP

48 HP

Frequently Asked Questions

How many HP is 10 amps at 240V?

For a three-phase motor with 90% efficiency and 0.85 power factor: HP = (√3 × 240 × 10 × 0.9 × 0.85) ÷ 746 = 4.3 HP approximately.

Why do I need efficiency and power factor?

How do I find motor efficiency?

Check the motor nameplate or manufacturer specifications. NEMA Premium efficiency motors typically range from 85-96% depending on size. Standard motors are 2-4% lower.