Amps to Watts Calculator
Convert current in amps to power in watts for AC or DC circuits.
Please note: For planning and educational use only. Electrical installation is governed by wiring regulations and is dangerous when done incorrectly. Always have work designed, installed and inspected by a qualified electrician.
What the Amps to Watts Calculator does
Power is voltage times current, reduced by power factor on AC circuits and multiplied by √3 for three-phase. This is the reverse of the watts-to-amps calculation and is useful when reading a breaker or meter rating.
Formula
DC: P = V × IAC single phase: P = V × I × PFAC three phase: P = √3 × V × I × PF
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Supply type | one of 3 options | Yes | — |
| Current | A | Yes | Accepts more than 0. |
| Voltage | V | Yes | Accepts more than 0. |
| Power factor | number | In some modes | Accepts 0.01 or more, up to 1. Shown Supply type is AC single phase, or Supply type is AC three phase. |
| Rate per kWh | selected currency | Optional | Accepts 0 or more. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Supply type and Currency.
- Enter Current and Voltage.
- Fill in the remaining inputs the form shows for your choice.
- Optionally add Rate per kWh.
- Select Calculate.
Worked example
A 10 A load on a 230 V single-phase supply at 0.95 power factor.
- Supply
- AC single phase
- Amps
- 10
- Voltage
- 230
- Power factor
- 0.95
Apparent 2,300 VA, real power 2,185 W, or about 2.93 horsepower.
Frequently asked questions
Why is real power lower than apparent power?
Because reactive current flows without doing useful work. Only the in-phase component of current delivers real power.
Method and sources
Method. Power from current and voltage, with the power factor and phase relationships applied.
Applies to. None for the arithmetic; installation work is governed by national wiring regulations
Assumptions
- Steady-state operation at the voltage and power factor entered.
Limitations
- Real power and apparent power diverge as power factor falls; billing and cable sizing do not always use the same one.
- Supply voltage varies within a tolerance band, so the figure moves with it.
Sources
- The national wiring regulations applying where the installation is located — Varies by country. The practical application; the relationship itself is standard circuit theory.