Pipe Diameter Calculator
Estimate the inside pipe diameter needed to carry an entered flow at a selected target velocity, with area, rounded reference size and pipe cost.
Default project preview
1.28 in
Required flow area
1.28 in²
Velocity at rounded ID
3.63 ft/s
Design flow
20 gal/min
Pipe length
100 ft
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Flow area = volumetric flow ÷ target velocity. Inside diameter = √(4 × area ÷ π). The reference diameter is rounded up by the entered increment.
FAQ
Pipe Diameter Calculator questions
Is nominal pipe size the same as inside diameter?+
No. Inside diameter varies with material, schedule, pressure class and wall thickness.
Should pressure loss also be checked?+
Yes. A diameter that meets velocity may still create too much friction loss over the full system.
Why round the diameter up?+
Rounding up gives a planning reference, but the available product size and actual inside diameter must be verified.