How to Calculate Transformer Sizing
What is Transformer Sizing?
Transformer Sizing Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
kVA = (Volts × Amps) / 1000 for single-phase; ×1.732 for three-phase
Step-by-Step Guide
- 1Calculate load kVA, add 20% safety margin for transformer sizing
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
480V, 100A, three-phase
Result
kVA = (480×100×1.732)/1000 = 83.1 → use 100 kVA
Common Mistakes to Avoid
- ✕Not applying code-required safety factors or derating
- ✕Forgetting to account for waste and cut losses in material estimates
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