# Flow Rate Calculator

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

Page: https://freecalculator.tech/tools/flow-rate-calculator
Last reviewed: 2026-11-03

## Formula

Q = A × v, with A = π × D² ÷ 4.

- 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.

## Inputs

- Pipe inside diameter
- Mean velocity

## Worked example: 50 mm pipe at 1.5 m/s

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

## Common questions

### Why inside diameter?

Fluid only flows through the bore; wall thickness varies by pipe schedule.

### 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.

### 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.

## 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.

## Sources

- OpenStax (Rice University) — https://openstax.org/details/books/university-physics-volume-1

## Cite this page

- APA: Free Calculator. (2026, November 3). Flow Rate Calculator. https://freecalculator.tech/tools/flow-rate-calculator
- MLA: "Flow Rate Calculator." Free Calculator, 3 Nov. 2026, https://freecalculator.tech/tools/flow-rate-calculator.
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