Flow Rate Calculator

Calculate flow rate step by step: Q = A × v, with A = π × D² ÷ 4.

In short

Formula: Q = A × v, with A = π × D² ÷ 4.

Flow rate

2.9452 L/s

m³/h: 10.6029
US gal/min: 46.683
Pipe area: 19.635 cm²

What this calculator does

Calculate flow rate step by step: Q = A × v, with A = π × D² ÷ 4. Worked example, questions and limitations included.

Use it to turn Pipe inside diameter, Mean velocity into a checked result you can compare, copy, or rerun with different assumptions.

The page shows the formula, a numeric worked example, and the assumptions that affect this fluid calculation.

Inputs and what they mean

Pipe inside diameter: — number value.
Mean velocity: — number value.

How to use it

Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
Check the breakdown to see every intermediate step.
Read the limitations before relying on the result.

Formula

Use the inside diameter.

Velocity is the mean across the section.

1 m³/s = 1,000 L/s = 15,850 US gal/min.

Q = A × v, with A = π × D² ÷ 4.

Inputs used: Pipe inside diameter, Mean velocity.

Worked example

50 mm pipe at 1.5 m/s

A = π × 0.05² ÷ 4 = 0.001963 m².
Q = 0.001963 × 1.5 = 0.002945 m³/s = 2.95 L/s.

Reading the result

The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.

Limitations and assumptions

Full, circular pipe.
Mean velocity only.
Incompressible fluid.
Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
The result depends on the values you enter for this flow rate calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

Common questions

Why inside diameter?

Fluid only flows through the bore; wall thickness varies by pipe schedule. Check the formula, example, and limitations on this page before using the result for a real fluid decision.

Is this volumetric or mass flow?

Volumetric. Multiply by density for mass flow.

What velocity is typical?

Design guides vary by fluid and service; many water systems aim for a few metres per second or less to limit noise and erosion. Check the formula, example, and limitations on this page before using the result for a real fluid decision.

How do I use the Flow Rate Calculator?

Enter the required values for Pipe inside diameter, Mean velocity. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

What formula does the Flow Rate Calculator use?

Q = A × v, with A = π × D² ÷ 4. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.

Can the Flow Rate Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.