How to Calculate Pump Sizing
What is Pump Sizing?
Pump Sizing Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
Pump HP = (Flow GPM × Total Head ft) / (3960 × Pump Efficiency)
Step-by-Step Guide
- 1Calculate total head (static + friction + pressure), select pump curve
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
50 GPM, 100 ft total head, 70% efficiency
Result
HP = (50 × 100)/(3960 × 0.70) = 1.8 HP
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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