Velocity and Hazen-Williams friction loss by flow for DN50 pipe. Loss values are in bar per 100 m, calculated on an internal diameter of roughly 52.5 mm.
Typical use: Distribution line; a medium sprinkler group.
Velocity and friction loss table (DN50)
| Flow (L/min) | Velocity (m/s) | C=100 | C=120 | C=140 |
|---|---|---|---|---|
| 50 | 0.38 | 0.070 | 0.050 | 0.038 |
| 100 | 0.77 | 0.254 | 0.181 | 0.136 |
| 150 | 1.15 | 0.537 | 0.384 | 0.288 |
| 200 | 1.54 | 0.915 | 0.653 | 0.491 |
| 300 | 2.31 | 1.938 | 1.383 | 1.040 |
| 400 | 3.08 | 3.299 | 2.355 | 1.770 |
| 600 | 4.62 | 6.985 | 4.985 | 3.748 |
| 800 | 6.16 | 11.893 | 8.488 | 6.382 |
| 1200 | 9.24 | 25.181 | 17.971 | 13.512 |
The C factor represents internal pipe roughness. Standards give different C values by pipe material and system type; a lower C for dry systems is common.
The calculation
Hazen-Williams in metric form: p = 6.05 × 105 × Q1.85 / (C1.85 × d4.87), where p is bar/m, Q is L/min and d is the internal diameter in mm.
The relation has two consequences:
- Doubling the flow raises the loss by roughly 3.6 times (21.85).
- Going up one pipe size cuts the loss dramatically; loss falls with the 4.87 power of diameter.
Internal diameter matters, not nominal size. The table values assume an internal diameter of roughly 52.5 mm. Pipes of a different wall thickness have a different bore and a correspondingly different loss; a precise calculation must use the pipe's own technical data.
Velocity check
High velocity brings noise, water hammer and long-term erosion. The velocity column lets you see at a glance whether the chosen size stays in a reasonable range. Where the velocity comes out too high, the answer is a larger diameter.
How to use it
- Determine the flow through this pipe section in the hydraulic calculation.
- Read the bar per 100 m loss from the table at the appropriate C value.
- Scale it to the actual length of the section.
- Add the equivalent lengths of fittings and valves.
- Add the elevation difference as static pressure.
Frequently Asked Questions
What C factor applies to DN50 pipe?
The value the standard gives for the pipe material and system type. The table has separate columns for C=100, 120 and 140; a lower C for dry systems is common.
What happens to the loss if flow doubles?
It rises by roughly 3.6 times (2^1.85). Flow increases therefore affect loss more than expected.
Is the nominal size the same as the bore?
No. The table assumes an internal diameter of roughly 52.5 mm; a different wall thickness changes the bore and the loss.
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Download MEP Calc on the App StoreNFPA 13 (2025) · BS EN 12845:2015+A1:2019. Values are calculated from Hazen-Williams using an approximate internal diameter; a precise calculation must use the pipe's technical data and the C factor the standard requires.