Pressure Drop Calculator
Calculate pressure loss in pipes using the Hazen-Williams equation for plumbing systems.
Results
Visualization
How It Works
Pressure drop in pipes is caused by friction between the water and pipe walls. The Hazen-Williams equation is the industry standard for calculating friction losses in water distribution systems.
The Formula
hf = 10.67 x L x Q^1.852 / (C^1.852 x D^4.87)
Variables
- hf — Head loss in feet of water
- L — Pipe length in feet
- Q — Flow rate in ft3/s
- C — Hazen-Williams coefficient
- D — Inside diameter in feet
Worked Example
For 10 GPM through 100 ft of 3/4" copper (C=140): hf = 10.67 x 100 x 0.02228^1.852 / (140^1.852 x 0.0625^4.87) = significant loss. Consider 1" pipe.
Practical Tips
- Keep pressure drop under 4 PSI per 100 feet
- Each 90-degree elbow adds approximately 2-3 feet of equivalent length
- Old pipes have lower C-factors due to scale buildup
- Pressure drop increases exponentially with flow rate