Pipe Flow Velocity Calculator
Find the average velocity in a pipe from the flow rate, or the flow that gives a target velocity. Choose a standard NPS Schedule 40 or 80 pipe or enter your own inside diameter.
- Area = π ÷ 4 × D² = π ÷ 4 × 0.10226² = 0.008213 m²
- Velocity = Q ÷ A = 0.013889 m³/s ÷ 0.008213 m² = 1.691 m/s
Typical design velocities (rules of thumb)
| Service | Typical velocity |
|---|---|
| Water, pump suction | 0.6 to 1.5 m/s |
| Water, pump discharge and general lines | 1.5 to 3 m/s |
| Viscous oils | 0.5 to 1.5 m/s |
| Saturated steam | 20 to 40 m/s |
| Compressed air and gases | 10 to 20 m/s |
Pipe Velocity Formula
Where v is the average velocity (m/s), Q the volumetric flow (m³/s), A the internal area (m²) and D the inside diameter (m). Always use the inside diameter, which depends on the pipe schedule, not the nominal size.
Worked example
50 m³/h of water in a 4 inch Sch 40 pipe (ID 102.26 mm): A = π ÷ 4 × 0.10226² = 0.008213 m². Q = 50 ÷ 3600 = 0.01389 m³/s, so v = 0.01389 ÷ 0.008213 = 1.69 m/s.
Frequently Asked Questions
What is a good water velocity in a pipe?
For general water service 1.5 to 3 m/s is common. Lower velocities waste pipe size, while higher ones increase pressure drop, noise and erosion.
What is the inside diameter of a 2 inch Schedule 40 pipe?
A 2 inch Sch 40 pipe has an OD of 60.33 mm and a wall of 3.91 mm, so the inside diameter is 52.50 mm.
Why does velocity matter for flow meters?
Every meter has a minimum velocity for accurate readings and a maximum before wear or noise. Checking velocity at minimum and maximum flow is the first step in flow meter sizing.
Learn more on the blog
What factors affect the stability of flow meter readings?
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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