Pipe Friction Loss Calculator
Water loses pressure as it moves through a pipe, because friction along the walls slows it. This estimates that loss as head, the height of water the friction is worth, for water in a pipe of a given size and length.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
The Hazen-Williams formula takes the flow, the pipe length and the inside diameter, and divides by the roughness factor raised to a power. Flow entered per minute is converted to cubic metres per second in the calculation.
The roughness factor C is lower for rougher or older pipe and higher for smooth new pipe. A common figure for new plastic pipe is 150. Enter the value that matches your pipe.
Worked example
Water moving 10 gal per minute through 100 ft of pipe with an inside diameter of 0.82 in loses about 20.67 ft of head to friction.
Questions
What is head loss?
It is the drop in pressure from friction, written as a height of water. It can be turned into a pressure drop for the same pipe and flow.
Does this include fittings and valves?
No. Fittings and valves add loss of their own. Add their equivalent pipe lengths to the pipe length to include them.
Why does a small change in diameter matter so much?
Friction loss falls steeply as the diameter grows, so a slightly larger pipe can cut the loss a lot.
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