# AC Wattage Calculator

URL: https://speedycalculator.com/calculators/physics/ac-wattage/
Last updated: 2026-10-30

> The AC wattage calculator finds the real power drawn by a single-phase or three-phase AC load from the voltage, current and power factor.

## Inputs

- Current type
- Voltage (V, kV, mV)
- Current (A, mA, µA, kA)
- Power factor

## Results

- Real power
- Apparent power
- Reactive power

## Formula

```
1-phase: P = V·I·PF · 3-phase (line-to-line): P = √3·V_LL·I·PF · 3-phase (line-to-neutral): P = 3·V_LN·I·PF
```

## Explanation

In AC circuits, voltage times current gives apparent power (VA). Only part of it does useful work – the real power in watts – depending on the power factor. Motors typically have a power factor of 0.8–0.9; heaters 1.

### How to use the AC Wattage Calculator

- **Current type**
- **Voltage**
- **Current**
- **Power factor**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose the system, enter the voltage, current and power factor.

### Inputs explained

FieldWhat to enterCurrent typeChoose one: Single-phase, Three-phase, line-to-line voltage, Three-phase, line-to-neutral voltageVoltageUnits: V, kV, mVCurrentUnits: A, mA, µA, kAPower factorA number

### What each result means

- **Real power** = [k]×[Voltage]×[Current]×[Power factor]
- **Apparent power** = [k]×[Voltage]×[Current]÷1000
- **Reactive power** = [k]×[Voltage]×[Current]×sqrt(1 - [Power factor]^2)÷1000

### Example values

How the main result changes when **Voltage** changes and everything else stays at the example values above:

Voltage (V)Real power (W)1151,092.5172.51,638.752302,185287.52,731.253453,277.54604,370

## Worked example

Inputs — Current type: Single-phase; Voltage: 230 V; Current: 10 A; Power factor: 0.95.

Results — **Real power = 2,185 W**; Apparent power = 2.3 kVA; Reactive power = 0.71817 kVAR.

## Key terms

- **Apparent power**: V × I, in volt-amperes.

## FAQ

**What is power factor?**
The ratio of real to apparent power, cos φ.

**Why √3 for three-phase?**
Line-to-line voltage is √3 times the phase voltage.

**Why are watts less than VA?**
Reactive current flows back and forth without doing work.

**What power factor should I assume?**
1 for heaters, 0.8–0.95 for motors and electronics.


## Sources

- [OpenStax – University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)