Line and Phase Voltage Calculator (Star and Delta)
By Santaji GadepatilinUpdated October 28, 2026
In a three-phase system, line values are measured between lines and phase values across each winding or load. In star (wye), line voltage is √3 times phase voltage; in delta, line current is √3 times phase current. This line and phase voltage calculator converts both ways — see star vs delta connection explained.
How to use the line and phase voltage calculator
Choose star or delta, enter the line voltage and line current (or the phase values, using the × buttons), and the power factor. The calculator gives the phase voltage and current and the total three-phase power.
Line and phase formulas
| Connection | Voltage | Current |
|---|---|---|
| Star (wye) | VL = √3 × Vph | IL = Iph |
| Delta | VL = Vph | IL = √3 × Iph |
P = √3 × VL × IL × PF = 3 × Vph × Iph × PF
Common system voltages
| Line voltage | Phase (line–neutral) voltage | Where |
|---|---|---|
| 208 V | 120 V | North America (commercial) |
| 380 V | 219 V | Older IEC, parts of Asia |
| 400 V | 231 V | Europe, IEC standard |
| 415 V | 240 V | India, UK, Australia |
| 440 V | 254 V | Marine, older Indian plants |
| 480 V | 277 V | North America (industrial) |
| 690 V | 398 V | Large motors, mining |
| 11000 V | 6351 V | MV distribution |
| 33000 V | 19053 V | Sub-transmission |
Motor windings
A motor nameplate marked Δ 415 V / Y 690 V has windings rated at 415 V. On a 415 V supply it runs in delta, and can be started in star (where each winding gets 240 V) — the basis of the star-delta starter. See the motor starting current calculator.
Frequently asked questions
What is the relationship between line and phase voltage in star?
V_line = √3 × V_phase. A 415 V system has about 240 V from each line to neutral.
What about delta?
Line and phase voltages are equal, but line current is √3 times the phase (winding) current.
Is three-phase power different for star and delta?
No. P = √3 × V_L × I_L × PF for both, using line values.
Why is 400 V three-phase paired with 230 V single-phase?
Because 400 ÷ √3 ≈ 230 V — the single-phase supply is one phase of the star system.