Pipe Velocity and Line Sizing Calculator
See the flow velocity in each Schedule 40 pipe size for your flow rate and pick the smallest line that stays within your velocity limit. Useful for line sizing and for checking flowmeter sizes.
Download
- Calculator sheet with a worked example
- How to Use sheet with steps
- 35 built in formulas, no macros
- Yellow input cells, grey results
- Calculation sign off block
- Excel, Google Sheets and LibreOffice
Worked Example
These are the results of the example already filled in the workbook. Replace the yellow cells with your own data.
Velocity in each line size (Schedule 40)
| NPS | DN | Inside diameter (mm) | Area (m²) | Velocity (m/s) | Within limits |
|---|---|---|---|---|---|
| 1/2" | 15 | 15.80 | 0.000196 | 85.01 | CHECK |
| 3/4" | 20 | 20.93 | 0.000344 | 48.44 | CHECK |
| 1" | 25 | 26.64 | 0.000557 | 29.90 | CHECK |
| 1 1/2" | 40 | 40.89 | 0.001313 | 12.69 | CHECK |
| 2" | 50 | 52.50 | 0.002165 | 7.70 | CHECK |
| 3" | 80 | 77.92 | 0.004769 | 3.50 | CHECK |
| 4" | 100 | 102.26 | 0.008213 | 2.03 | OK |
| 6" | 150 | 154.05 | 0.018639 | 0.89 | OK |
| 8" | 200 | 202.72 | 0.032276 | 0.52 | OK |
| 10" | 250 | 254.51 | 0.050874 | 0.33 | CHECK |
| 12" | 300 | 303.23 | 0.072216 | 0.23 | CHECK |
About this Calculator
Velocity is the quickest check of a line size or a flowmeter size: too high causes erosion, noise and pressure loss; too low causes settling and poor meter accuracy. Seeing every size at once makes the choice obvious.
Basis: Schedule 40 inside diameters from ASME B36.10M wall thickness. Velocity v = Q ÷ A.
How to use
- Enter the flow rate and the minimum and maximum acceptable velocity for the service.
- Read the velocity in each Schedule 40 size.
- The smallest size within the limits is selected automatically; also check pressure drop for long lines.
Formulas used
- A = π ÷ 4 × ID².
- v = Q (m³/h) ÷ 3600 ÷ A.
Related tools
Frequently Asked Questions
What velocity should water have in a pipe?
Roughly 1.5 to 3 m/s for pump discharge and 0.6 to 1.5 m/s for suction lines.
Why size a magmeter smaller than the line?
To raise the velocity into the 1 to 3 m/s range where the meter is most accurate.
Are these inside diameters for Schedule 40?
Yes, calculated from ASME B36.10M outside diameter and Schedule 40 wall thickness.
Learn more on the blog
Types of flow meters
A practical guide on instrumentationblog.in that explains the engineering behind this workbook.
Read Full Article