Convert between pipe velocity and volumetric flow rate across various units.
Pipe velocity is the mean flow speed through a pipe section, calculated from volumetric flow rate divided by cross-section area. This calculator returns velocity in m/s and ft/s from flow rate and inside diameter, helping you check whether a sizing meets the velocity envelope for water service (3–8 ft/s), hydraulic suction (under 4 ft/s), pressure (10–15 ft/s), and return (15–20 ft/s).
v = Q / A where Q is volumetric flow and A is cross-section area. For circular pipe A = π × D² / 4. Unit conversion is the most error-prone step: 1 GPM through 1 inch² is 0.32 ft/s. Inside diameter must be the actual ID, not the nominal pipe size — Schedule 40 1-inch is 26.6 mm ID (not 25.4). The calculator handles both NPS-Schedule and DN inputs. Safe-velocity bands: water suction 3–8 ft/s, water discharge 4–10 ft/s, hot water 1.5–4 ft/s to limit erosion, hydraulic oil suction 1.5–4 ft/s, hydraulic pressure 10–15 ft/s, hydraulic return 5–10 ft/s. Air or gas service runs at much higher velocity (60–120 ft/s) but with mach-number checks.
A facilities engineer designing a 90 °C circulating loop limits velocity to 1.2 m/s (below the 1.5 m/s erosion threshold for copper) and upsizes a 32 mm tube to 42 mm where the design 80 lpm gives 0.96 m/s.
A power-unit builder sizes a 100 lpm pump suction; in 1-inch tube velocity is 3.3 m/s (exceeds 1.5 limit), so the designer chooses 1.5-inch which gives 1.3 m/s and clears NPSH-required margin.
A food-process technician verifying a 50 mm tubular heat exchanger at 200 lpm computes 1.7 m/s, confirming sanitary cleaning velocity, then notes that 250 lpm would shift it above the 2.0 m/s spec.
Water: 3-8 ft/s suction, 4-10 ft/s discharge. Hot water: 1.5-4 ft/s. Hydraulic oil: 1.5-4 ft/s suction, 10-15 ft/s pressure, 5-10 ft/s return. Air: 60-120 ft/s. Always compare to manufacturer guidelines.
Volumetric flow / area gives the cross-sectional mean velocity. Peak velocity in laminar flow is 2× mean (parabolic profile). In turbulent flow peak is only 1.2× mean. For friction-loss calculations the mean velocity is the correct input.
Roughness doesn't change v = Q/A but it does change the friction factor and hence ΔP for a given v. The velocity envelope itself assumes commercial-finish pipe.