Pipe Size / Flow Rate Converter
Cross-sectional area and GPM, L/min and CFM conversions.
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Flow rate
58.75 GPM
At 6.00 fps through a 2.000 in bore
This is a theoretical volumetric flow from area and velocity. Real systems lose capacity to friction, fittings and elevation, so size pipework from a pressure-drop calculation for anything critical.
58.8 GPM · 222.4 L/min · 3.142 sq in
How this is calculated
Volumetric flow is the pipe's cross-sectional area multiplied by the average fluid velocity. Area comes from the internal diameter:
area = π × (diameter ÷ 2)²
flow = area × velocity
Everything is computed in SI internally — metres and metres per second give cubic metres per second — then converted out: multiply by 15,850.32 for US gallons per minute, by 60,000 for litres per minute, and by 2,118.88 for cubic feet per minute.
Use the actual bore, not the nominal size. A nominal 2 inch schedule 40 steel pipe has an internal diameter of about 2.067 inches, while schedule 80 is only 1.939 inches — a 12% difference in flow area. Because area scales with the square of the diameter, going up one pipe size roughly doubles capacity at the same velocity.
Keep design velocities sensible: 5–8 ft/s (1.5–2.4 m/s) for domestic water supply, under 4 ft/s on suction lines, and under 2 ft/s for gravity drainage. Excessive velocity causes water hammer, noise and long-term erosion of fittings and elbows.