About the Power Calculator
What is the Power Calculator?
This electrical power calculator works out the real power a load uses from voltage, current and power factor, for DC, single-phase or three-phase supplies.
It also shows apparent and reactive power, and the energy used per day and per month – the units on your electricity bill.
How to use the Power Calculator
- Supply (sample: Single-phase AC)
- Voltage (V) (sample: 230)
- Current (A) (sample: 10)
- Power Factor (AC only) (sample: 0.9)
- Hours of Use per Day (sample: 8)
- Press Calculate Electrical Power (results also refresh as you type). The result card shows the Real Power, along with Apparent power, Reactive power, In kilowatts and Energy per day.
Formula used
P = V × I × PF (single-phase); P = √3 × V × I × PF (three-phase)
- Apparent power S = V × I (or √3 × V × I)
- Reactive power Q = √(S² − P²)
- Energy (kWh) = P × hours ÷ 1,000
For DC, power factor is 1 and P = V × I.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Supply | Single-phase AC |
| Voltage (V) | 230 |
| Current (A) | 10 |
| Power Factor (AC only) | 0.9 |
| Hours of Use per Day | 8 |
| Result | Value |
|---|---|
| Real Power | 2,070 W |
| Apparent power | 2,300 VA |
| Reactive power | 1,002.5 VAR |
| In kilowatts | 2.07 kW |
| Energy per day | 16.56 kWh |
| Energy per month (30 days) | 496.8 kWh |
Tips for using the Power Calculator
- Motors and older fluorescent fittings have power factors of 0.7–0.9; resistive heaters are 1.0.
- One kWh is one "unit" on an Indian electricity bill.