Transformer Sizing Calculator
Select the correct transformer kVA rating for multiple loads with demand factor and growth
Results
Total Connected Load
—
Design Load (with demand+growth)
—
% Loading at Recommended Size
—
Total kW
—
Recommended: — kVA
Formula Reference
Each Load kVA = Load kW / Power Factor
Total Connected kVA = Σ (Load_i kW / PF_i)
Design kVA = Total kVA × (Demand Factor / 100) × (1 + Growth / 100)
Standard Sizes (kVA): 15, 25, 37.5, 45, 50, 75, 100, 112.5, 150,
167, 225, 300, 500, 750, 1000
Recommended = next standard size ≥ Design kVA
% Loading = Design kVA / Recommended kVA × 100
Total Connected kVA = Σ (Load_i kW / PF_i)
Design kVA = Total kVA × (Demand Factor / 100) × (1 + Growth / 100)
Standard Sizes (kVA): 15, 25, 37.5, 45, 50, 75, 100, 112.5, 150,
167, 225, 300, 500, 750, 1000
Recommended = next standard size ≥ Design kVA
% Loading = Design kVA / Recommended kVA × 100
Worked Example
Three loads: HVAC (50 kW, PF=0.85), Lighting (30 kW, PF=1.0), Motors (40 kW, PF=0.80). Demand factor 90%, Growth 25%.
| Load | kW | PF | kVA |
|---|---|---|---|
| HVAC | 50 | 0.85 | 58.8 |
| Lighting | 30 | 1.00 | 30.0 |
| Motors | 40 | 0.80 | 50.0 |
| Total | 120 kW | — | 138.8 kVA |
| Design kVA | 138.8 × 0.90 × 1.25 = 156.1 kVA | ||
| Recommended | 167 kVA transformer (93.5% loading) | ||