Power Calculator
Calculate power P in watts and kilowatts from current, voltage, and power factor cos φ. Single-phase and three-phase AC, DC current.
Network type
Mains 220 V, 380 V, or any other value
Current consumed by the load
AC networks: 0.95 typical, 1 for purely resistive loads
Calculation formula
P = U × I × cos φ
Single-phase AC: multiply voltage by current and by the power factor.
About the power calculator
This calculator finds active electrical power from current and voltage. Three modes are supported: single-phase AC mains (110/220 V), three-phase AC (380/400 V), and DC.
For AC the power factor cos φ is taken into account — it represents the share of active power and depends on the load. Heaters and incandescent lamps have cos φ ≈ 1, motors and PSUs typically 0.85–0.95.
All calculations run locally in your browser, your data is not sent to a server. The result is shown in watts and kilowatts so you can immediately use it to size circuit breakers or cable cross-section.
Benefits
Three modes in one
Single-phase AC, three-phase AC, and DC — switch with a single radio button.
Power factor support
cos φ is included in the formula automatically for AC networks.
Result in W and kW
Two units at once — handy for breaker selection and energy bill estimates.
FAQ
How do I calculate power from current and voltage?
For DC and resistive single-phase AC, P = U × I. For inductive AC loads multiply by cos φ. In a three-phase network with line-to-line voltage, P = √3 × U × I × cos φ.
Which cos φ value should I use?
Use 1 for purely resistive loads (heaters, incandescent lamps, electric stoves). For most household appliances and induction motors, 0.85–0.95. Switching power supplies without PFC can be as low as 0.5–0.7.
How is three-phase calculation different?
With line-to-line voltage of 380/400 V, the formula gains the √3 ≈ 1.732 multiplier. So the same current in a three-phase circuit delivers roughly 1.73× more power than in a single-phase 220 V line.
How do I get current to size a breaker?
Use the inverse formula: I = P / (U × cos φ). For 220 V single-phase with P = 3 kW and cos φ = 0.95, current ≈ 14.4 A — a 16 A breaker fits.
When is DC mode used?
For batteries, solar panels, 12/24 V LED strips, low-voltage systems and PSU outputs. In DC there is no power factor, so P = U × I.