Free Water Pressure Drop Calculator
Estimate friction-related pressure drop in a straight pipe using the Darcy-Weisbach simplified approach.
ft
in
GPM
Pressure Drop
2.70 psi
Flow Velocity4.08 ft/s
Head Loss6.22 ft
Pressure Drop vs Pipe Length
Darcy-Weisbach Pressure Drop
h_f = f x (L / D) x (V squared / 2g)
Where f is the Darcy friction factor, L is pipe length, D is diameter, V is velocity, and g is gravitational acceleration (32.174 ft/s squared). Multiply head loss in feet by 0.4333 to convert to psi.
Example Calculation
100 ft of 1-inch pipe carrying 10 GPM, friction factor 0.02.
- 01D = 1/12 = 0.0833 ft
- 02Area = pi x 0.04167 squared = 0.005454 sq ft
- 03V = (10/448.831) / 0.005454 = 4.09 ft/s
- 04h_f = 0.02 x (100/0.0833) x (4.09 squared / 64.348) = 6.24 ft
- 05Pressure drop = 6.24 x 0.4333 = 2.70 psi
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