Pipe Flow Rate
Cross-sectional area times speed is the volumetric flow. Double the diameter and the area quadruples, so the flow quadruples too — which is why widening a pipe beats raising the pressure.
Your numbers
Flow rate
176.7L/min
Area
19.63cm²
Litres
10,603L
Formula
Flow rate = π × (Pipe bore ÷ 200) ² × Flow speed (m/s) × 60000
Use the internal bore. Pipe is usually specified by outside or nominal diameter, so subtract the wall thickness.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Pipe bore (cm)The inside diameter of the pipe, not the outside. | 5 | 0 and up |
| Flow speed (m/s)How fast the water moves through the pipe. | 1.5 | 0 and up |
Step by step
Quick reference table
Results when only Pipe bore (cm) changes and everything else stays put.
| Pipe bore (cm) | Flow rate (L/min) | Area (cm²) | Litres (L) |
|---|---|---|---|
| 2.5 | 44.2 | 4.91 | 2,651 |
| 3.75 | 99.4 | 11.04 | 5,964 |
| 5 | 176.7 | 19.63 | 10,603 |
| 7.5 | 397.6 | 44.18 | 23,856 |
| 10 | 706.9 | 78.54 | 42,412 |
What each result means
| Result | At default values |
|---|---|
| Flow rate (L/min)The volume of water passing per unit of time. | 176.7 |
| Area (cm²)The space a shape covers — length squared. | 19.63 |
| Litres (L)Capacity in litres; one litre is 1,000 cm³. | 10,603 |
Common mistakes
Use the internal bore. Pipe is usually specified by outside or nominal diameter, so subtract the wall thickness.
Glossary
- Pipe bore
- The inside diameter of the pipe, not the outside.
- Flow speed (m/s)
- How fast the water moves through the pipe.
- Flow rate
- The volume of water passing per unit of time.
- Area
- The space a shape covers — length squared.
- Litres
- Capacity in litres; one litre is 1,000 cm³.
Frequently asked questions
Q. How is Pipe Flow Rate calculated?
Flow rate = π × (Pipe bore ÷ 200) ² × Flow speed (m/s) × 60000 — Cross-sectional area times speed is the volumetric flow. Double the diameter and the area quadruples, so the flow quadruples too — which is why widening a pipe beats raising the pressure.
Q. Can you walk through an example?
With Pipe bore 5cm, Flow speed (m/s) 1.5, the answer is Flow rate 176.7L/min.
Q. What do I need to enter?
Enter Pipe bore, Flow speed (m/s). The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Pipe bore (cm) moves the answer to Pipe bore (cm) 2.5 → Flow rate (L/min) 44.2 and Pipe bore (cm) 10 → Flow rate (L/min) 706.9. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Use the internal bore. Pipe is usually specified by outside or nominal diameter, so subtract the wall thickness.
Related calculators
Keep your length units consistent across inputs — mixing centimetres and metres throws results far off.