# Amps to Horsepower Calculator

Enter amps, volts, and motor efficiency to calculate the horsepower.

## Power:

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## How to Convert Amps to Horsepower

The conversion from amps, a measure of electric current, to horsepower, a measure of power output by a motor, can be done using a fairly simple formula.

P_{(HP)} = I_{(A)} × V_{(V)} × η × PF / 746

Thus, the power *P* in horsepower is equal to the current *I* in amps times the voltage *V* in volts times the efficiency *η* times the power factor *PF*, divided by 746.^{[1]}

How did we get that? This formula can be derived in two steps.

### Step One: Calculate the Power

Since horsepower is a measure of electric power, Watt’s Law can be used to convert. Watt’s Law gives us the formula to solve power given voltage, current, and AC power factor using this formula.

P_{(W)} = I_{(A)} × V_{(V)} × PF

The formula states that the power *P* in watts is equal to the current *I* in amps times the voltage *V* in volts times the power factor *PF*.

One additional consideration that should be made when doing the conversion is the efficiency of the motor being used. Motors are often only 80% to 90% efficient, which means that they can only produce 80% to 90% of energy output for the amount of power in.

When converting to horsepower, the efficiency can be accounted for by multiplying the result by the efficiency *η* in decimal form.

P_{(W)} = I_{(A)} × V_{(V)} × PF× η

### Step Two: Convert the Power to Horsepower

After converting amps and volts to watts, the next step is to convert watts to horsepower. The table below offers a quick reference for how to convert watts to electrical or mechanical horsepower.

Horsepower | Watts |
---|---|

1 Electric HP | 746 watts |

1 Mechanical HP | 745.7 watts |

1 Metric HP | 735.5 watts |

Because 1 horsepower is equal to 746 watts, the formula above will include a division by 746 to complete the conversion.

P_{(HP)} = P_{(W)} / 746 ^{W}⁄_{HP}

**For example,** let’s find the horsepower of a motor drawing 8 amps at 120 volts that is 90% efficient. Assume a PF of 1.

P_{(HP)} = 8 A × 120 V × 0.9 × 1 / 746 ^{W}⁄_{HP}

P_{(HP)} = 864 W / 746 ^{W}⁄_{HP}

P_{(HP)} = 1.158 HP

## Common Amps to Horsepower Conversions

Amps | Horsepower | Voltage | Efficiency |
---|---|---|---|

1 A | .14 HP | 120 V | 90% |

2 A | .29 HP | 120 V | 90% |

3 A | .43 HP | 120 V | 90% |

4 A | .58 HP | 120 V | 90% |

5 A | .72 HP | 120 V | 90% |

6 A | .87 HP | 120 V | 90% |

7 A | 1.01 HP | 120 V | 90% |

8 A | 1.16 HP | 120 V | 90% |

9 A | 1.3 HP | 120 V | 90% |

10 A | 1.45 HP | 120 V | 90% |

15 A | 2.17 HP | 120 V | 90% |

20 A | 2.9 HP | 120 V | 90% |

25 A | 3.62 HP | 120 V | 90% |

30 A | 4.34 HP | 120 V | 90% |

We also have a horsepower to amps calculator that you may find useful.

## References

- Miller, C., NFPA's Electrical References,
*National Fire Protection Association*, 2004, Jones & Bartlett Learning, 67-75. https://www.google.com/books/edition/NFPA_s_Electrical_References/raUyIi7i-asC