Free · Electronics and circuits calculators 🔌

Single and Three-Phase Apparent Power, Voltage and Line Current

Relate RMS voltage, line current and total apparent power for single-phase or balanced three-phase AC, with both voltage conventions and inverse inputs.

  • Formula & worked example
  • Private in your browser
  • No signup
Go to tool

Calculator inputs

Loading calculator…

How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

For balanced three-phase power of 3 kVA and 100 V line-to-neutral, each line carries 10 A. For single-phase 1 kVA at 100 V, current is also 10 A.

Single-phase: S = VI; balanced three-phase: S = √3 VLL I = 3 VLN I.

Worked example

Enter these known values and leave the other values blank.

Three-phase voltage convention
Line-to-neutral
Total apparent power S
3 kVA
RMS voltage V
100 V
RMS line current I
10 A

Assumptions and limitations

  • Use RMS voltage and line current magnitudes. S is total apparent power in VA, not real power in W; 1 kVA = 1,000 VA. Three-phase modes assume balanced sinusoidal operation.
  • Choose line-to-line or line-to-neutral RMS voltage explicitly in three-phase mode. For a balanced supply, VLL = √3 VLN. The displayed current is current in each line, not a sum of the three currents.
  • Positive apparent power requires positive voltage and current in this finite model. Mode choices are categorical settings; keep them selected while solving a missing numeric value. Clear the unknown before entering an inverse.
  • No power factor or motor efficiency is applied to apparent power. This model does not calculate starting current, neutral current, imbalance, harmonics, conductor size, protection or equipment ratings.

Common questions

Which voltage should I enter?

Select its convention first. Use RMS line-to-line voltage for that choice or RMS line-to-neutral voltage for the other. In balanced three-phase operation the two voltages differ by √3.

Is the current total across all three phases?

No. The result is RMS current in each line for the balanced model. Total three-phase power already includes the three phases.

Can I solve a different missing quantity?

Yes. Keep the categorical phase and voltage choices selected, clear the missing numeric value and enter enough independent known values. Unlock a numeric default before solving for it.

References

The line-to-line balanced three-phase factor uses √3 rounded once to 64 significant decimal digits instead of the captured 12-digit approximation. Mode choices remain explicit; positive apparent or shaft power requires positive voltage and line current.

Explore electronics and circuits calculators 🔌 or browse all physics calculators.