Flow Rate Calculator
Calculate flow rate step by step: Q = A × v, with A = π × D² ÷ 4.
In short
Calculate flow rate step by step: Q = A × v, with A = π × D² ÷ 4.
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.
You enter pipe inside diameter and mean velocity, and the flow rate calculator shows the answer along with the working, so you can check it or try other numbers.
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.
Reference: OpenStax (Rice University)
Last reviewed:
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.
Sources
Method based on OpenStax (Rice University).
Cite this page
Free Calculator. (2026, November 3). Flow Rate Calculator. https://freecalculator.tech/tools/flow-rate-calculator
"Flow Rate Calculator." Free Calculator, 3 Nov. 2026, https://freecalculator.tech/tools/flow-rate-calculator.
Flow Rate Calculator — Free Calculator, https://freecalculator.tech/tools/flow-rate-calculator
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