AC Wattage Calculator — Single-Phase and Three-Phase Power
The AC Wattage Calculator converts single-phase and three-phase voltage, current, and power factor to watts. Our tool allows you to input the values you have and returns the answer instantly — no need to remember a single formula. If you are curious about how we arrive at these answers, scroll down for full formula explanations.
Definition of Wattage
Are those electrical terms a constant puzzle? Wattage is the amount of electric power required to run an electrical appliance. The unit of measurement is the watt (W), named after Scottish inventor James Watt.
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 bulb uses 25 watt-hours (or 0.025 kilowatt-hours) of electricity per hour — and that is what goes on your energy bill.
What Does AC Mean?
There are two different types of electrical current: AC and DC.
AC stands for Alternating Current. It is the type of electricity that reverses its direction with a particular frequency (50 Hz in Europe and Russia, 60 Hz in the USA). AC moves in waves — its amplitude rises and falls periodically. Alternating current is the type of electricity that goes to our homes, schools, and businesses and is transmitted over long distances.
DC (Direct Current) flows in one direction only and does not change over time. It is used over short distances to power batteries, electronics, and devices such as phones, laptops, and electric vehicles.
What You Need to Calculate AC Wattage
To calculate AC wattage, you need three values:
- Current (Amperes, A) — the flow of electric charge through the circuit.
- Voltage (Volts, V) — the electrical potential difference driving the current.
- Power Factor (PF) — a number between 0 and 1 that accounts for the phase difference between current and voltage in AC circuits. A power factor of 1 means the most efficient use of power; 0 means no useful power is transferred. The default in this calculator is 0.95, which is typical for most appliances.
You also need to know the type of AC circuit:
- Single-phase (household outlets in most of the world)
- Three-phase line-to-line (industrial equipment, phase-to-phase voltage)
- Three-phase line-to-neutral (industrial equipment, phase-to-neutral voltage)
How to Calculate AC Wattage — Single-Phase
The formula for single-phase AC power:
Where:
- P — Power in watts (W)
- PF — Power factor (0 to 1)
- I — Electrical current in amperes (A)
- U — Voltage in volts (V)
Example: Calculate the wattage for 24 V and 3.75 A with a power factor of 0.5:
How to Calculate AC Wattage — Three-Phase Line-to-Line
Three-phase power is used in industrial applications, electric motors, and large commercial buildings. When you know the line-to-line voltage (voltage between two phases), use this formula:
Example: A three-phase motor draws 15 A at 400 V (line-to-line) with a power factor of 0.9:
How to Calculate AC Wattage — Three-Phase Line-to-Neutral
When you know the line-to-neutral voltage (voltage from one phase to the neutral wire), use this formula:
Example: A balanced three-phase load with 10 A per phase at 230 V (line-to-neutral), PF = 0.85:
Unit Systems Supported
This calculator supports both metric (SI) and American unit systems:
| Quantity | Metric / SI | American |
|---|---|---|
| Current | mA, A, kA | mA, A, kA |
| Voltage | mV, V, kV | mV, V, kV |
| Power output | W, kW, MW | W, kW, MW, BTU/hr, HP |
Energy Cost Calculator
Enable the optional Electricity Cost section to estimate your running costs. Enter how many hours per day the device runs and your local electricity price per kWh. The calculator supports the following currencies:
- $ USD — US Dollar
- ₽ RUB — Russian Ruble
- € EUR — Euro
- £ GBP — British Pound
- ¥ JPY — Japanese Yen
- ¥ CNY — Chinese Yuan
- ₹ INR — Indian Rupee
- R$ BRL — Brazilian Real
The cost calculation formula is:
Frequently Asked Questions
What is a good power factor?
A power factor of 0.9 or above is considered good for most industrial equipment. Home appliances typically range from 0.6 to 0.99. Purely resistive loads (heaters, incandescent bulbs) have a power factor of 1.0.
Why does three-phase use √3 in the formula?
In a balanced three-phase system, the line-to-line voltage is √3 times the line-to-neutral voltage. The factor √3 ≈ 1.732 comes from the geometry of the phase relationships in a three-phase system (120° apart).
What is the difference between watts and volt-amperes (VA)?
Watts (W) measure real power — the actual work done. Volt-amperes (VA) measure apparent power — the total power drawn from the supply. The relationship is: W = VA × PF. In DC circuits, PF = 1, so watts and VA are the same.
How do I convert watts to kilowatts?
Divide by 1,000: 1 kW = 1,000 W. To convert to megawatts, divide by 1,000,000.