Pipe Sizing Calculator
Diameter from Flow Rate
Calculate pipe diameter from flow rate and velocity
Velocity from Pipe Size
Calculate velocity given pipe diameter and flow
Formula
D = sqrt(4Q / (pi x V)) | Q = GPM / 448.831 (ft3/s) | V = Q / A
Frequently Asked Questions
What velocity should water pipes have?
Residential water pipes should have velocities between 2-8 ft/s. The ideal range is 4-6 ft/s. Velocities above 8 ft/s can cause water hammer and erosion.
How do I convert GPM to pipe size?
Convert GPM to cubic feet per second (divide by 448.831), divide by target velocity to get area, then calculate diameter. Round up to the next standard pipe size.
Does pipe material affect sizing?
Yes. Different materials have different inside diameters for the same nominal size and different roughness values that affect friction losses.
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