Magnetic Flow Meter Sizing Calculator
Choose the right electromagnetic flow meter size. The calculator shows the flow velocity at minimum and maximum flow for each standard DN size and highlights sizes in the recommended range.
- v = Q ÷ (π/4 × DN²) for each size
- Recommended: max velocity 1 to 6 m/s with min velocity at least 0.3 m/s
Velocity by meter size
| Size | At min flow | At max flow | Assessment |
|---|---|---|---|
| DN 10 | 17.7 m/s | 212 m/s | Too fast |
| DN 15 | 7.86 m/s | 94.3 m/s | Too fast |
| DN 20 | 4.42 m/s | 53.1 m/s | Too fast |
| DN 25 | 2.83 m/s | 34 m/s | Too fast |
| DN 32 | 1.73 m/s | 20.7 m/s | Too fast |
| DN 40 | 1.11 m/s | 13.3 m/s | Too fast |
| DN 50 | 0.707 m/s | 8.49 m/s | Acceptable |
| DN 65 | 0.419 m/s | 5.02 m/s | Recommended |
| DN 80 | 0.276 m/s | 3.32 m/s | Too slow |
| DN 100 | 0.177 m/s | 2.12 m/s | Too slow |
| DN 125 | 0.113 m/s | 1.36 m/s | Too slow |
| DN 150 | 0.0786 m/s | 0.943 m/s | Too slow |
| DN 200 | 0.0442 m/s | 0.531 m/s | Too slow |
| DN 250 | 0.0283 m/s | 0.34 m/s | Too slow |
| DN 300 | 0.0196 m/s | 0.236 m/s | Too slow |
| DN 350 | 0.0144 m/s | 0.173 m/s | Too slow |
| DN 400 | 0.0111 m/s | 0.133 m/s | Too slow |
| DN 450 | 0.00873 m/s | 0.105 m/s | Too slow |
| DN 500 | 0.00707 m/s | 0.0849 m/s | Too slow |
| DN 600 | 0.00491 m/s | 0.0589 m/s | Too slow |
Sizing Rule
Recommended: 1 to 6 m/s at maximum flow, at least 0.3 m/s at minimum flow
The bore is taken as equal to the nominal DN, which is close enough for sizing. Check the actual liner bore for exact velocity.
Worked example
For 5 to 60 m³/h, DN 65 gives 0.42 to 5.0 m/s, inside the recommended band. DN 80 would also work at 0.28 to 3.3 m/s, but the minimum velocity drops below 0.3 m/s.
Frequently Asked Questions
What velocity is best for a magnetic flow meter?
Around 1 to 5 m/s at normal flow. Most meters measure from about 0.3 to 10 m/s, but accuracy is best above about 1 m/s.
Should a mag meter be the same size as the pipe?
Not necessarily. Size for velocity; a smaller meter with reducers often performs better at low flow.
What about abrasive slurries?
Keep velocity lower, about 2 to 3 m/s maximum, to reduce liner and electrode wear, but high enough to keep solids suspended.
Learn more on the blog
What factors affect the stability of flow meter readings?
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
Read Full Article