Power Calculator
Solve power, voltage, current and resistance from any two known values, then estimate hourly energy consumption in kWh.
About This Calculator
Electrical power in a DC circuit is the product of voltage and current. Given any two of voltage, current and resistance, the calculator derives the remaining values and computes power draw plus the energy consumed over a chosen operating time.
Watt and kWh
Power is expressed in watts (W) — the instantaneous rate of energy use. Multiply by time in hours and divide by 1000 to express battery or utility consumption in kilowatt-hours (kWh).
How to Use
- Select which two quantities you know from the dropdown.
- Enter the two known values; the third is derived automatically.
- Optionally set operating time to see kWh energy consumption.
- For AC circuits with power factor, the true power is P = V·I·cos(φ) — this calculator models DC / resistive AC.
Formulas
| Power | P = V × I |
| Resistance from V & I | R = V / I |
| Energy | E = P × t (Wh), kWh = E / 1000 |
Design Notes
For AC loads with reactive components, use P = V·I·PF where PF is the power factor.
Buck-boost style energy ratings: always use RMS values of V and I for AC power.