Pipe flow rate calculator
Flow is area times velocity. Everything else in pipe sizing follows from keeping the velocity sensible.
m/s
L/min
Flow rate
34.21L/min
- In US gallons per minute
- 9.038
- Velocity for the target flow
- 1.3153 m/s
- Bore area
- 0.000 380 1 m2
- Litres per metre of pipe
- 0.3801
- Reynolds number
- 32 868
- Time to fill 100 litres
- 2:55
Show the working
- Inside diameter = 22
- Velocity = 1.5
- Or a flow rate = 30
- Bore area = pi * (22/1000)^2 / 4 = 0.000 380 133
- flow_m3s = 0.000 380 133 * 1.5 = 0.000 570 199
- Flow rate = 0.000 570 199 * 60000 = 34.2119
- In US gallons per minute = 34.2119 / 3.785411784 = 9.037 84
- Velocity for the target flow = 0.000 380 133 > 0 ? 30 / 60000 / 0.000 380 133 : 0 = 1.315 33
- Litres per metre of pipe = 0.000 380 133 * 1000 = 0.380 133
- Reynolds number = 1.5 * 22/1000 * 998 / 0.001002 = 32 868.3
- Time to fill 100 litres = 34.2119 > 0 ? 100 / 34.2119 * 60 : 0 = 175.377
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- flow = area x velocity
- area = pi d^2 / 4
Above about 2.5 m/s water pipework gets noisy and, in copper, erosion-corrosion becomes a real risk.