Transformers & motors
Transformer Turns Ratio Calculator
For an ideal transformer, voltage ratio equals turns ratio and is inverse to current ratio. Real losses and regulation are outside this relationship.
Calculate ideal voltage, turns, and inverse current relationships between transformer windings.
Calculated result
Ideal transformer ratio
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
What this calculator returns
Real transformers have losses, regulation, impedance, and thermal limits that the ideal ratio does not model.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Vp/Vs = Np/Ns = Is/Ip for an ideal transformer.
- 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.
V is winding voltage, N is turns count, and I is current magnitude.
Worked example
| Input | Value |
|---|---|
| Primary voltage | 120 V |
| Secondary voltage | 12 V |
120 V primary and 12 V secondary gives an ideal 10:1 turns ratio; 1 A primary corresponds to 10 A secondary ideally.
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
Why is current ratio inverse to voltage ratio?
In an ideal transformer, approximately conserved power means the lower-voltage winding carries proportionally more current.
Does this include transformer losses?
No. The relationship is ideal and excludes winding resistance, core loss, regulation, saturation, and magnetizing current.
Assumptions and limitations
- Ideal transformer only.
- No protection, conductor, or loading recommendation.
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 .