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hp to amps Calculator

Created by Wojciech Sas, PhD
Reviewed by Steven Wooding
Last updated: Jan 18, 2024


This is the hp to amps calculator, a great tool that helps you convert hp to amps for an electric motor (or any other device). It's essentially similar to the watts to amps calculator, but at the same time, you don't have to worry about switching between units!

In the article, you can find a short description of what is horsepower, what it means to convert horsepower to amps, and the formulas for hp to amps conversion, depending on the current type.

Last but not least – our tool can also work as an amps to hp calculator! You can choose which values to input and which you want to find!

What does it mean to convert hp to amps?

Hp stands for horsepower – the unit of, well, power. Similarly, the amps represent the amperage, which refers to the electric current measured in amperes.

Whenever you face the challenge of converting horsepower to amps, you are about to estimate the output current from a device with a well-defined power.

Analogically, if you try to convert amps to hp, you should evaluate the power by knowing the output current.

Great! As we've just established what the hp to amps calculation is, it's high time asking how to do the task.

How to convert horsepower to amps? Hp to amps formulas

According to Ohm's law, the output current I is a ratio of the power P and the output voltage V. However, it changes a bit in real-life applications, as any power engine works with a certain efficiency, η. Knowing that we can write the hp to amps formula for direct current (DC) as:

I = P × 746 / (V × η).

As the SI unit of power is the watt, it's common to use power converter before estimating the amperage. A rule of thumb states that you should multiply the power in hp by 746 to get the power in watts. Here we are assuming you're using electrical horsepower (for mechanical horsepower, the factor is circa 745.7).

However, using our hp to amps calculator, you don't need to bother about unit conversion at all, as the tool converts between units automatically, so simply choose the one you work with!

The hp to amps calculations change a little for alternating current (AC). We can distinguish three different cases:

  1. Single-phase AC:

    I = P × 746 / (V × PF × η)

  2. Three-phase AC, line-to-line voltage:

    I = P × 746 / (√3 × V × PF × η)

  3. Three-phase AC, line-to-neutral voltage:

    I = P × 746 / (3 × V × PF × η).

PF is the power factor that tells us about the nature of the source. It ranges from 0 to 1. The resistive-only loads result in values close to unity. You can find a more detailed description with examples in Omni's power factor calculator.

💡 It's possible to switch between line-to-line and line-to-neutral systems using delta-to-wye conversion.

The unit conversion rule applies here as well, so if you want to work out the formulas by hand, don't forget to multiply the outcome by factor 746.

How to use the hp to amps calculator?

Let's say we want to find the current flow in an AC single-phase motor. The engine's designed power is 1 hp, and it works with a voltage equal to 200 V. The engine's efficiency is 90%, while the power factor is 0.92. Let's work out the result step by step using the appropriate horsepower to amps formula:

  1. Estimate the power in watts (the nominator of the expression), 1 hp × 746 = 746 W.

  2. Evaluate the product in the denominator, 200 V × 0.92 × 90% = 165.6 V. You can always convert a decimal to percent to make your life easier (90% = 0.9).

  3. Make a fraction of these numbers and find the final horsepower to amps value, 746 / 165.6 = 4.505 A. We round the outcome to four significant figures.

  4. In this case, a 1 hp motor to amps gives 4.505 A.

You can also use our tool as an amp to hp calculator. Take a look at the following example:

What is the motor's nominal power if it runs with the applied three-phase line-to-line voltage of 100 V, the flowing current equals 0.5 A, while the efficiency and power factor are 95% and 0.8, respectively? Let's see how to solve it:

  1. Rearrange the formula of hp to amps for the three-phase line-to-line system P = I × √3 × V × PF × η / 746.

  2. Apply the values (we can approximate the square root of 3 as 1.73), P = 0.5 × 1.73 × 100 × 0.8 × 95% / 746.

  3. The resulting power equals 0.088 hp.

  4. We can also rewrite the outcome using scientific notation, P = 8.8×10⁻² hp. And that's how you convert amps to hp!

Note that we are using approximations in these calculations, so we strongly recommend using our hp to amps calculator to get the precise results!

FAQ

What does horsepower mean?

The term horsepower(hp), created by James Watt, refers to a unit of measurement of power, and it is mainly applied to engines. It refers to the power needed to move 550 pounds one foot in one second or equivalently to the power necessary to move 33,000 pounds one foot in one minute.

How do I convert hp to amps?

You can follow these steps to convert hp to amps:

  1. Multiply the power P by 746 to change it from hp to watts: 746 × P.
  2. Divide the result by the output voltage V.
  3. If you are working with DC, divide the result by the efficiency η.
  4. If you are working with AC, divide the result by the product η × PF, where PF is the power factor.

The result is the current in amperes.

What is the difference between hp and amps?

The term hp refers to horsepower. It is a specific unit of power, corresponding to approximately 746 watts in SI units.

Amps stand for a unit of electric current measured in amperes. One ampere is equivalent to an electric charge of 1 coulomb moving past a point in one second.

How many amps does a 12V 1HP motor draw?

You can convert a 1 hp motor operating with 12 V to amps by considering the following steps:

  1. Multiply 1 hp by 746 to transform it in watts: 1 × 746 = 746.
  2. Divide the result by the voltage: 746/12 = 62.17.
  3. Divide the result by the efficiency. Usually, a 12 V DC motor works with 55% efficiency: 62.17/0.55 = 113.03 amps.
Wojciech Sas, PhD
Current type
DC
Power (hp)
hp(E)
Voltage (V)
V
Efficiency (η)
%
Amperage (amps)
A
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