Pipe Flow & Water Velocity Calculator

Water velocity is a quick check on pipe size: high velocity causes noise, water hammer and erosion, especially in hot water copper lines.

Important: Plumbing sizing is governed by the plumbing code adopted in your area (for example the IPC or UPC) and local amendments. This result is an engineering estimate, not a code determination.

Tapeline — Pipe Flow & Water Velocity Calculator

Printed September 29, 2026

CalculateVelocity from flow
Pipe inside diameter0.785 in
Flow rate8 gpm
Velocity5 ft/s

Results update as you type.

Use the actual inside diameter, not the nominal size. ¾ in type L copper ≈ 0.785 in.

gpm
ft/s

How it’s calculated

  • Velocity (ft/s) = 0.4085 × GPM ÷ ID² (in)
  • GPM = velocity × ID² ÷ 0.4085

Worked example

8 gpm through ¾ in type L copper (0.785 in ID).

Inputs

Calculate
Velocity from flow
Pipe inside diameter
0.785 in
Flow rate
8 gpm
Velocity
5 ft/s

Results

Water velocity
5.3 ft/s
Flow rate
8 gpm

Load this example into the calculator

Assumptions and limits

  • Full pipe, incompressible water flow.

Verify the result against the applicable local code, adopted code edition, manufacturer instructions and project requirements. See our methodology.

Questions

What is a good water velocity in pipes?

Common guidance is up to about 8 ft/s for cold water and 5 ft/s for hot water in copper to limit noise and erosion. Manufacturer and code limits vary.

How much water can a ¾ inch pipe carry?

At 8 ft/s, ¾ in type L copper (0.785 in ID) carries about 12 gpm; at 5 ft/s, about 7.5 gpm.