How do I calculate pipe flow rate?

Find the pipe area from diameter, then multiply by average velocity: v.

Why does velocity increase in a smaller section?

For steady incompressible flow, Q stays approximately constant, so velocity rises when area falls.

Does this calculate pressure drop?

No. Pressure drop requires pipe length, roughness, viscosity, fittings and a friction model.

Flow Rate Calculator

Calculate volumetric flow rate from area and velocity, solve velocity or pipe size, use continuity, estimate tank fill time and Torricelli orifice flow.

Use the pipe inside diameter: outside size without wall thickness overstates flow.

This calculator does not calculate flow from pressure, pipe length, roughness, or head loss.

One liter per minute equals 0.06 m³/h; one cubic meter per hour is about 16.667 L/min.

Pipe section

Solve for

Inside diameter

Flow velocity

Also calculate mass flow from liquid density

Volumetric flow rate

The core pipe-flow estimate multiplies average velocity by cross-sectional area. The same relationship can solve flow rate, velocity or required area.

Q = A v

Q is volumetric flow rate, A cross-sectional area and v average velocity.

\overset{m}{˙} = ρQ

Mass flow rate is density times volumetric flow rate.

Scope limits

No friction-pressure sizing

This page does not calculate Darcy-Weisbach, Hazen-Williams or pump curves. Use it for geometry, velocity, continuity, fill time and simple orifice estimates.

Frequently Asked Questions

Sources and References

Calculations are based on the listed reference sources. Links open in a new tab.

Updated: June 2, 2026

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