Electrical basics
Single-phase current calculator
Enter the power, voltage and power factor of a single-phase load to see the approximate current, apparent power and reactive power. For a first estimate only.
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P: active power, Q: reactive power, S: apparent power. The lower the cos φ, the longer the Q side. Not to scale.
How is it calculated?
For a single-phase load the current follows from active power, line-to-neutral voltage and power factor.
Current
I = P × 1000 / (U × cos φ)
P: active power (kW), U: line-to-neutral voltage (V), cos φ: power factor, I: current (A).
Apparent and reactive power
S = P / cos φ; Q = S × sin φ
S: apparent power (kVA), Q: reactive power (kVAr), sin φ = √(1 − cos² φ).
Example
- Inputs: P = 3 kW, U = 230 V (example voltage; depends on your grid), cos φ = 0.95.
- Current: 3 × 1000 / (230 × 0.95) ≈ 13.7 A.
- Apparent power ≈ 3.16 kVA; reactive power ≈ 0.99 kVAr.
The example inputs are for illustration only; they are not verified defaults. Results are approximate and do not replace engineering advice.
Frequently asked questions
What power factor should I use for a heater?
Purely resistive loads such as heaters have a power factor of about 1. Motor-driven and electronic devices are lower; check the nameplate.
Why do I have to enter the voltage?
Supply voltage differs between countries and grids (for example 120 V or 230 V). The calculator does not assume one; enter your own value.
Is this enough to choose a breaker?
No. Protection also depends on the cable, inrush current and short-circuit conditions. This result is only the approximate running current.
What about three-phase loads?
Use the three-phase current calculator; its formula uses √3 and the line-to-line voltage.