Transformers & motors
Transformer kVA Calculator
Transformer-side current equals apparent power divided by voltage. Balanced three-phase current also divides by the square root of three.
Calculate transformer current from kVA and voltage for single-phase or balanced three-phase systems.
Calculated result
Transformer current
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
What this calculator returns
This is the kVA-current relationship, not a protection or conductor-sizing output.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
I = 1000 × kVA/V (1φ); I = 1000 × kVA/(√3 × VLL) (3φ).
- P
- Real or mechanical power, as identified by the calculator.
- S
- Apparent power in VA or kVA.
- V
- Winding, line, or load voltage.
- I
- Winding, line, or estimated input current.
- PF
- Entered power factor where real and apparent power differ.
- η
- Entered conversion or motor efficiency.
Use the voltage for the transformer side whose current you want.
Worked example
| Input | Value |
|---|---|
| Phase | Three-phase AC |
| Transformer rating | 75 kVA |
| Side voltage | 480 V |
A 75 kVA, 480 V three-phase side carries about 90.21 A at rated apparent power in the ideal balanced relationship.
Reference table
| Apparent rating | 240 V single-phase | 480 V three-phase |
|---|---|---|
| 1 kVA | 4.17 A at 240 V 1φ | 1.20 A at 480 V 3φ |
| 5 kVA | 20.83 A at 240 V 1φ | 6.01 A at 480 V 3φ |
| 10 kVA | 41.67 A at 240 V 1φ | 12.03 A at 480 V 3φ |
| 25 kVA | 104.17 A at 240 V 1φ | 30.07 A at 480 V 3φ |
Frequently asked questions
Should I enter primary or secondary voltage?
Enter the line voltage on the side where you want the current estimate, using the corresponding phase selection.
Does transformer kVA include power factor?
kVA is apparent power, so power factor is not needed to calculate line current from the transformer rating.
Assumptions and limitations
- No impedance, losses, temperature rise, regulation, breaker, fuse, or conductor sizing.
Method and sources
Review the electrical formulas, calculation methodology, and standards status for the references most relevant to this calculation. The broader technical sources index records source scope and verification. Last reviewed .