Technical Tables and Calculators

Pipe Size and Flow Rate Tables: DN Sizes and m³/h Capacities

Flow rates at 1.5 and 2.5 m/s by DN and bore for steel, plastic and stainless pipes, plus flow and volume tables for compressed air lines.

ORFA Technical TeamUpdated: Oct 30, 20265 min read

A pipe size and flow rate table shows how many cubic metres per hour a pipe can carry at a given velocity and is the starting point for pipe sizing in pump, booster set and plumbing projects. Flow is the internal cross-section multiplied by velocity, so even at the same DN, the bore – which varies with material and wall thickness – directly affects the result.

On this page you will find DN sizes, bores and flow rates at 1.5 m/s and 2.5 m/s for steel, plastic (PPR/PVC) and stainless steel pipes, plus flow and free-air volume tables for compressed air lines.

How Is Flow Rate Calculated?

Q (m³/h) = v (m/s) × π × d² / 4 × 3600 (d: bore in metres)

For example, a DN50 steel pipe with a 53.0 mm bore carries 1.5 × π × 0.053² / 4 × 3600 ≈ 11.9 m³/h at 1.5 m/s. In liquid lines 1–2 m/s is considered economical; 2.5 m/s can be used as an upper limit, while higher velocities increase noise, wear and the risk of water hammer.

Pipe Size and Flow Rate Tables for Liquids

Steel Pipes (Black Steel; DN10–DN100 DIN 2440 / EN 10255 Medium Series, DN150–DN200 EN 10220)

DN	Outside diameter (mm)	Wall thickness (mm)	Bore (mm)	Flow @ 1.5 m/s (m³/h)	Flow @ 2.5 m/s (m³/h)	Friction loss @ 1.5 m/s (m WC/100 m)
10	17.2	2.35	12.5	0.66	1.10	30.5
15	21.3	2.35	16.6	1.17	1.95	21.2
20	26.9	2.65	21.6	1.98	3.30	15.1
25	33.7	3.25	27.2	3.14	5.23	11.3
32	42.4	3.25	35.9	5.47	9.11	7.9
40	48.3	3.25	41.8	7.41	12.35	6.6
50	60.3	3.65	53.0	11.91	19.86	4.9
65	76.1	3.65	68.8	20.08	33.46	3.5
80	88.9	4.05	80.8	27.69	46.15	2.9
100	114.3	4.50	105.3	47.03	78.38	2.1
150	168.3	4.50	159.3	107.63	179.38	1.3
200	219.1	5.90	207.3	182.26	303.76	0.9

Plastic Pipes (PPR / PVC / U-PVC)

DN	Outside diameter (mm)	Bore (mm, approx.)	Flow @ 1.5 m/s (m³/h)	Flow @ 2.5 m/s (m³/h)	Friction loss @ 1.5 m/s (m WC/100 m)
10	16	13.0	0.72	1.19	24.7
15	20	16.6	1.17	1.95	18.2
20	25	21.0	1.87	3.12	13.5
25	32	27.2	3.14	5.23	9.8
32	40	33.8	4.85	8.08	7.5
40	50	42.6	7.70	12.83	5.6
50	63	53.0	11.91	19.86	4.3
65	75	65.8	18.36	30.60	3.3
80	90	81.6	28.24	47.07	2.6
100	110	103.6	45.52	75.87	1.9
150	160	154.6	101.37	168.95	1.2
200	225	205.6	179.28	298.80	0.8

Stainless Steel Pipes (304 / 316)

DN	Outside diameter (mm)	Bore (mm, approx.)	Flow @ 1.5 m/s (m³/h)	Flow @ 2.5 m/s (m³/h)	Friction loss @ 1.5 m/s (m WC/100 m)
15	21.3	17.3	1.27	2.12	17.9
25	33.7	29.7	3.74	6.24	9.1
50	60.3	55.3	12.97	21.62	4.2
80	88.9	84.9	30.57	50.95	2.5
100	114.3	108.3	49.74	82.91	1.9
150	168.3	163.3	113.10	188.50	1.1
200	219.1	215.1	196.23	327.05	0.8

Flow rates are calculated from the bore. Friction losses are for 1.5 m/s and water at 15 °C, using Darcy-Weisbach / Colebrook-White (roughness: black steel 0.045 mm, plastic 0.007 mm, stainless 0.015 mm). Plastic pipe bores vary with PN/SDR class, so the bores listed are approximate.

Tip: At the same velocity, friction loss per 100 m is much higher in small pipes (at 1.5 m/s, about 21 m WC in DN15 steel versus about 2 m WC in DN100). On long lines, check the size against total pressure loss, not velocity alone.

Pipe Size and Flow for Compressed Air

Compressed Air Flow by Air Velocity (m³/h)

Values are the volumetric flow of air in the line at working pressure (velocity × internal cross-section). Velocities of around 6–8 m/s are commonly used in main distribution lines to limit pressure drop.

Air velocity (m/s)	DN15	DN25	DN40	DN65	DN100	DN150
3	2.16	6.12	14.76	39.24	92.52	202.32
4	2.88	8.28	19.44	52.56	123.12	269.64
5	3.60	10.08	24.48	65.52	154.08	336.96
6	4.32	12.24	29.16	78.48	184.68	403.2
8	5.76	16.2	38.88	104.76	246.6	540.0

Volume of Free Air Under Pressure (dm³)

The volume of compressor free air delivery (FAD) at working pressure is approximately V_compressed = V_free / (p + 1) (p in bar g, atmospheric pressure taken as 1 bar; using 1.013 bar gives results about 1% higher).

Free air volume (dm³)	4 bar g (dm³)	6 bar g (dm³)	8 bar g (dm³)
5	1.0	0.71	0.56
10	2.0	1.43	1.11
25	5.0	3.57	2.78
50	10.0	7.14	5.56
100	20.0	14.29	11.11
200	40.0	28.57	22.22
500	100.0	71.43	55.56

Frequently Asked Questions

Is DN the inside diameter of the pipe?

No. DN (nominal size) is only a designation. The actual bore depends on the pipe standard, material and wall thickness; a DN50 steel pipe has a bore of about 53 mm, while a DN50 PPR/PVC pipe differs.

Which velocity should be used in liquid lines?

For domestic water and pump lines 1–2 m/s is usually economical. Lower velocities are preferred in pump suction lines to avoid cavitation.

Why do plastic pipes give a different flow at the same DN?

Plastic pipes have different outside diameters and wall thicknesses from steel pipes; as the bore changes, so does the flow at the same velocity. Always use the actual bore when sizing.

Conclusion

Basing pipe selection on the actual bore and a suitable velocity, rather than the DN alone, ensures both adequate flow and reasonable pressure loss. These tables allow quick preliminary sizing of liquid and compressed air lines. See our pipes product group for suitable pipes for your installation.

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