Head Loss Calculator

Head loss is the friction bill for moving water. It tells you how many feet of water column a pipe "eats" for every 100 feet of run - multiply by the real length and you have the pressure taxed out by friction alone.

Head Loss Calculator returns the Hazen-Williams friction loss per 100 ft along with the flowing velocity and the Reynolds number, so you can compare a 1/2 in line with a 3/4 in line before committing to either.

• Per-100-ft friction: Hazen-Williams loss for the line.
• Scale by length: Total friction for any run.
• Velocity: Feet per second at the given flow.
• Reynolds number: Confirms fully turbulent flow.
• Material C factor: Copper, plastic or aged steel.
• Export: Copy or download the report.

1. Enter the flow rate in GPM.
2. Enter the internal pipe diameter in inches.
3. Pick the material (C factor).
4. Optional: add a run length to see total friction for that length.
5. Compare sizes: change the diameter and watch head loss fall.

Example - 5 GPM in 3/4 in copper. At C=150, roughly 1.5-2 ft of head per 100 ft at a comfortable 3.7 fps. Push the same flow through a 1/2 in line and friction climbs steeply - one reason undersized legs starve a fixture group.

• Reference-grade numbers: Per-100-ft figures match traditional friction tables.
• Size pipes side by side: See diameter and flow trade-offs.
• Feed other estimates: Use the per-100-ft loss in run calculations.
• Free and private: No uploads, no logging.