How to Calculate Pressure Drop
What is Pressure Drop?
Pressure Drop Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
ΔP = f × (L/D) × (ρV²/2) using Darcy-Weisbach
Step-by-Step Guide
- 1Determine friction factor, pipe length, diameter, and flow velocity
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
100 ft of 1 inch pipe, 5 fps, water
Result
ΔP ≈ 4.3 PSI per 100 feet
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 Pressure Drop Calculator
Try it yourself →