Pipe pressure drop calculator
Friction loss rises steeply with flow and falls even more steeply with bore. Going up one pipe size can cut the loss by two thirds.
L/min
%
Total head required
7.168m
- Pressure
- 0.7029 bar
- Pressure in psi
- 10.195
- Friction head loss
- 4.168
- Loss in the straight run
- 3.087
- Loss per metre
- 0.102 90 m/m
- Flow velocity
- 1.315 m/s
- Pressure drop
- 70.29 kPa
Show the working
- Flow rate = 30
- Inside diameter = 22
- Pipe length = 30
- Hazen-Williams C = 140
- Allowance for fittings = 35
- Rise in elevation = 3
- flow_m3s = 30 / 60000 = 0.0005
- d_m = 22 / 1000 = 0.022
- Loss per metre = 10.67 * 0.0005^1.852 / (140^1.852 * 0.022^4.87) = 0.102 903
- Loss in the straight run = 0.102 903 * 30 = 3.0871
- Friction head loss = 3.0871 * (1 + 35/100) = 4.167 58
- Total head required = 4.167 58 + 3 = 7.167 58
- Pressure drop = 7.167 58 * 1000 * g0 / 1000 = 70.29
- Pressure = 70.29 / 100 = 0.7029
- Pressure in psi = 70.29 / 6.89475729316836 = 10.1947
- Flow velocity = pi * 0.022^2 / 4 > 0 ? 0.0005 / (pi * 0.022^2 / 4) : 0 = 1.315 33
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
Scenarios & local history
Compare a saved scenario
Recent calculations
The formula
- Hazen-Williams: head loss per metre = 10.67 Q^1.852 / (C^1.852 d^4.87)
- total head = friction + static lift
The exponent on diameter is -4.87, so a 10% larger bore cuts the loss by 38%.
Hazen-Williams applies to water at ordinary temperatures. Use Darcy-Weisbach for anything else.