A transformer's kVA rating determines its capacity. Proper sizing prevents overloading, overheating, and ensures efficient power delivery.
3φ: kVA = V × I × √3 ÷ 1000. 1φ: kVA = V × I ÷ 1000.
Choose a transformer rated 125% of your calculated kVA for safety margin.
Building power distribution, industrial plants, data centers, substations.
Consider future load growth — typically add 20–25% margin.
Calculate transformer size from voltage and current.
For single-phase: kVA = V × I ÷ 1000. √3 ≈ 1.732 accounts for 3-phase power.
3 steps to find the right transformer.
Identify primary/secondary voltage: 480V, 415V, 240V, etc.
Sum all load currents in amps. Add 25% margin for future growth.
kVA = V × I × √3 ÷ 1000 for 3-phase. Select next standard size up.
Common kVA ratings for distribution transformers.
| kVA | 415V 3φ Amps | 480V 3φ Amps | 240V 1φ Amps |
|---|---|---|---|
| 25 | 34.8 | 30.1 | 104.2 |
| 50 | 69.5 | 60.1 | 208.3 |
| 100 | 139.1 | 120.3 | 416.7 |
| 250 | 347.7 | 300.7 | 1,041.7 |
| 500 | 695.4 | 601.4 | 2,083.3 |
| 1000 | 1,390.9 | 1,202.8 | 4,166.7 |
Real-world transformer calculations.
415V, 200A 3-phase:
415 × 200 × 1.732 ÷ 1000 = 143.8 kVA → Select 150 kVA
480V, 600A 3-phase:
480 × 600 × 1.732 ÷ 1000 = 498.8 kVA → Select 500 kVA
240V, 100A single-phase:
240 × 100 ÷ 1000 = 24 kVA → Select 25 kVA
25 free conversion tools — each with its own unique calculator, interactive visuals, and detailed explanations.
Converter for kva-to-watts
Converter for kva-to-mw
Converter for kva-to-amps
Converter for kva-to-kwh
Converter for kva-to-hp
Converter for kva-to-va
Converter for kva-to-btu
Converter for kva-to-gw
Converter for kva-to-kw-3-phase
Converter for kva-to-joule
Converter for kva-to-kv
Converter for kva-to-ka
Converter for kva-to-mbh
Converter for kva-to-mwh
Converter for kva-to-mva
Converter for kva-to-rpm
Converter for va-to-v
Converter for kw-to-kwh
Converter for power-factor-calculator
Converter for transformer-kva-calculator
Converter for generator-size-calculator
Converter for kva-to-kvar
Converter for kvar-calculator
Converter for watts-to-kwh
Converter for voltage-drop-calculator
Common questions about transformer sizing.
Calculate kVA = V × I × √3 ÷ 1000 (3-phase), then select the next standard size with 25% margin.
Common sizes: 25, 50, 75, 100, 150, 225, 300, 500, 750, 1000, 1500, 2000, 2500 kVA.
Yes, but oversizing wastes money and increases losses. Stay within 125–150% of calculated load.
Overheating, shortened lifespan, voltage drops, possible fire hazard.
Always use kVA. Transformers are rated in apparent power, not real power.