The AC wattage calculator converts single-phase and three-phase voltage to watts. Our tool allows you to input the information you are hoping to convert and returns the answer without knowing a single formula. However, if you are interested in how we arrive at these answers, we also have the formulas used in our AC wattage calculator below with clear explanations on how to use each one.

For all those who find electrical terms confusing, this article also answers the questions:

  • What does AC mean?
  • What does wattage mean for a homeowner?
  • How to calculate wattage from volts and amps?

If you are a physics student, you may also be interested in our Ohm's law calculator.

Definition of the term wattage

Are those electrical terms a constant puzzle? Are you a student looking to answer the question, what does wattage mean? Most of us have heard the word, but its exact meaning may be a complete mystery.

Wattage is the amount of electric power required to run an electrical appliance. The unit of measurement for wattage is watts which have the abbreviation W.

Now, what does wattage mean to a homeowner? Each electrical appliance has a set amount of wattage. A device usually has the wattage stamped onto it. So if a light bulb is marked 25 watts, that light bulb contributes 25 watts-hours (or 0.025 kilowatts-hours) to the electrical bill in an hour.

What does AC mean and where do we use it?

There are two different types of power, AC and DC.

AC is the abbreviation for alternating current. It is the type of current that reverses its direction with a particular frequency. We use alternating current to transmit electric current over long distances.

We calculate AC differently depending on whether we use single-phase, three-phase line-to-line or three-phase line-to-neutral voltage.

Still not sure you can answer the question what does AC mean? Well, AC, or alternating current, moves in waves where its amplitude rises and falls periodically. Alternating current is the type of electricity that goes to our homes, schools, and businesses.

Direct current (DC) goes in one direction and does not change over time. We use it only over short distances to run our devices.

What do you need to know to calculate AC wattage?

To calculate the AC wattage (watts), you first need to establish whether you are using single-phase or three-phase current. If you are using a three-phase current, you also need to know its type. The two types of three-phase power are line-to-line and line-to-neutral.

We calculate wattage from volts and amps. To find the wattage, we need to:

  • Find out the number of amperes and volts the device uses.
  • Obtain the power factor. Check our electrical power calculator to learn more about it.
  • Then, using the relevant formula, substitute the values and calculate. Our formulas below will show you how to calculate wattage from volts and amps.

🙋 Try our volt to electron volt calculator if you are interested in learning more about conversions using volts.

How to calculate wattage from volts and amps using AC single phase current

Below is the AC single phase amps to watts calculation formula used by our AC wattage calculator:

  • P = PF × I × U


  • P – Power or wattage;
  • PF – Power factor;
  • I – Electrical current; and
  • U – Voltage.

This formula means that the wattage equals the power factor multiplied by the current multiplied by the voltage. We measure current in amperes (A) and voltage in volts (V).

The power factor varies from 0 to 1. One represents the most efficient use of power, while 0 means the opposite. The power factor in our calculator is set to 0.95 by default.

Let's look at an example using this AC single phase watts to amps calculation formula:

Calculate watts from 24 volts and 3.75 amperes with a power factor of 0.5. Using the AC watt formula, we have:

  • P = 0.5 × 3.75 × 24 = 45 W

Now, if you are interested in calculating the electricity consumption of the appliances in your home, our appliance wattage calculator is what you need.

🔎 Three-phase power is where three power lines alternate to take the current to your home. Each of these lines alternates their power at a different time. Only one of the three lines will be at its highest at any given time.

How to calculate wattage using AC three phase current for line-to-line voltage

When dealing with a three-phase current, we must first establish whether it is line-to-line or line-to-neutral voltage. Only then would we know how to calculate the wattage correctly. The formula below is strictly for the line-to-line voltage:

  • P = √3 × PF × I × V

This formula means that the wattage equals the square root of three multiplied by the power factor, current, and voltage. The voltage V refers this time to the line-to-line voltage.

Here is an example that uses this AC watt formula:

Calculate the watts from 120 volts and 5 amperes with a power factor of 0.8:

P = √3 × 0.8 × 5 × 120 = 831.38 W

How to calculate wattage using AC three phase current for line-to-neutral voltage

The following formula is the one used for the line-to-neutral voltage

  • P = 3 × PF × I × V

This formula means that the wattage equals two multiplied by the power factor, current, and line-to-neutral voltage.

We will look at the problem below to see this formula in use. Calculate the watts from 12 volts and 0.125 amperes with a power factor of 0.2:

P = 3 × 0.2 × 0.125 × 12 = 0.9 W

If you found this calculator helpful, you may also like this electricity cost calculator.

Adena Benn
Current type
AC single phase
Power factor
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