How to Calculate Generator Sizing
What is Generator Sizing?
Generator Sizing Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
Generator kW = Total Running Watts + Largest Motor Starting Watts
Step-by-Step Guide
- 1Sum all running loads, add starting surge for largest motor
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
5000W running + 3000W motor start
Result
Generator = 8000W → use 10kW generator
Common Mistakes to Avoid
- ✕Not applying code-required safety factors or derating
- ✕Forgetting to account for waste and cut losses in material estimates
Ready to calculate? Try the free Generator Sizing Calculator
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