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
| Field | What to enter |
|---|---|
| Current type | Choose one: Single-phase, Three-phase, line-to-line voltage, Three-phase, line-to-neutral voltage |
| Voltage | Units: V, kV, mV |
| Current | Units: A, mA, µA, kA |
| Power factor | A 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) |
|---|---|
| 115 | 1,092.5 |
| 172.5 | 1,638.75 |
| 230 | 2,185 |
| 287.5 | 2,731.25 |
| 345 | 3,277.5 |
| 460 | 4,370 |
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
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.
Frequently asked questions
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.