Hp to Amps Calculator

By Wojciech Sas, PhD candidate
Last updated: Dec 04, 2020

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 a similar thing to the conversion from wattage to amperage, 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 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 the 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 horsepowers 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 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 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 convert units 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 changes 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.

💡 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 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 next 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 to use our hp to amps calculator to get the precise results!

Wojciech Sas, PhD candidate