Required pipe bore for a target line velocity, with the resulting velocity and typical service velocity guidance.
A = Q/v; D = √(4A/π)
How it works
For a target line velocity, the required flow area is just flow divided by velocity, and the bore follows from the area. The tool then checks the target against typical velocity bands for the selected service so the size comes with a sanity check.
Worked example
50 m³/h at a 2 m/s target for a pump-discharge line. Needs about a 94 mm bore — round up to the next standard pipe so the actual velocity lands at or below 2 m/s.
Inputs
Flow rate (m³/h)
Target velocity (m/s)
Service (for guidance)
Frequently asked questions
What velocity should I size a liquid line for?
Common practice: 1–3 m/s for pump discharge and 0.3–1.5 m/s for pump suction (to protect NPSH). Staying below ~4 m/s avoids erosion, noise, and water hammer.
How about gas and steam lines?
Rough targets are 15–30 m/s for gas/vapor and 25–40 m/s for saturated steam, but these lines are ultimately limited by allowable pressure drop and noise, not velocity alone.
Why round up to a standard size?
The calculated bore rarely matches a real pipe. Choosing the next-larger standard size lowers the actual velocity slightly, which is the safe direction for erosion and pressure drop. See the Schedule 40/80 pipe dimensions reference.
Guidance bands are common process rules of thumb, not code requirements — gas and steam lines are ultimately limited by pressure drop, noise, and erosion.
Size on the actual pipe inside diameter (schedule dependent), not the nominal size.
References
Line-velocity guidance per common practice and API RP 14E (erosional-velocity concept for two-phase lines).
Related Fluid Mechanics tools
Pipe Pressure Drop — Frictional ΔP and head loss for single-phase flow in a circular pipe (Darcy–Weisbach, Swamee–Jain friction factor).
Fittings Pressure Drop (K-factors) — Minor losses through elbows, tees, and valves by the ΣK excess-head method — the companion to straight-pipe friction.
Pipe Velocity & Reynolds — Line velocity, Reynolds number, and flow regime from flow rate and pipe inside diameter.
Friction Factor (Moody) — Darcy (and Fanning) friction factor from Reynolds number and relative roughness — Colebrook–White solved exactly, with the Swamee–Jain explicit fit for comparison.