Size a duct
Calculate the diameter, airflow or air velocity of a duct, then compare standard diameters. Results are indicative: our engineering office confirms the sizing of the ductwork.
Diameter, airflow, velocity
Choose what you are looking for and enter the other two values: the calculation updates automatically.
Circular duct: airflow = velocity × cross-section. Pressure drop estimated for a galvanised duct (roughness 0.15 mm, air at 20 °C), 90° bends counted with a coefficient of 0.3.
| Standard diameter | Actual velocity | Pressure drop | Verdict |
|---|
Transport velocities taken from the INRS ED 695 guide (table VI) and, for wood, from the INRS ED 750 guide. The calculation uses the top of the range and recommends the standard diameter that does not fall below it.
We do not exceed 25 m/s in a duct: above that, the velocity is flagged as high.
Velocity too low: dust settles in the duct. High velocity: more noise and pressure drop. The diameter is chosen to maintain the conveying velocity.
Your list of ducts and fittings
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Transport velocities in ducts
Minimum values so that the pollutant does not settle in the ductwork, according to the INRS ED 695 guide.
| Pollutant | Examples | Minimum velocity |
|---|---|---|
| Fumes | Zinc and aluminium oxide fumes | 7 to 10 m/s |
| Very fine, light dust | Very fine cotton lint | 10 to 13 m/s |
| Dry dust and powders | Fine rubber dust, bakelite moulding dust, jute lint, cotton and soap dust | 13 to 18 m/s |
| Average industrial dust | Dry sanding abrasive, grinding dust, jute and granite dust, brick cutting, clay and limestone dust | 18 to 20 m/s |
| Wood (chips, sawdust, dust) | Woodworking machines, sanding, sawing, panel machining (INRS ED 750: 20 m/s target) | 20 m/s |
| Heavy dust | Dust from tumbling and shake-out barrels, sandblasting, cast iron boring | 20 to 23 m/s |
| Heavy or damp dust | Damp cement dust, fibre-cement pipe cutting dust, quicklime, wet pneumatic conveying | over 23 m/s |
Source: INRS, practical ventilation guide no. 0, ED 695, table VI “Range of minimum transport velocities for polluted air in ductwork”. Wood: INRS, practical ventilation guide no. 12, ED 750.
Airflows by duct diameter
Theoretical airflow in m³/h according to the internal diameter and air velocity.
| Diameter | 10 m/s | 13 m/s | 18 m/s | 20 m/s | 23 m/s | 25 m/s |
|---|---|---|---|---|---|---|
| Ø 100 mm | 285 | 370 | 510 | 565 | 650 | 705 |
| Ø 120 mm | 405 | 530 | 735 | 815 | 935 | 1 020 |
| Ø 150 mm | 635 | 825 | 1 150 | 1 270 | 1 460 | 1 590 |
| Ø 160 mm | 725 | 940 | 1 300 | 1 450 | 1 660 | 1 810 |
| Ø 200 mm | 1 130 | 1 470 | 2 040 | 2 260 | 2 600 | 2 830 |
| Ø 250 mm | 1 770 | 2 300 | 3 180 | 3 530 | 4 060 | 4 420 |
| Ø 300 mm | 2 540 | 3 310 | 4 580 | 5 090 | 5 850 | 6 360 |
| Ø 315 mm | 2 810 | 3 650 | 5 050 | 5 610 | 6 450 | 7 010 |
| Ø 400 mm | 4 520 | 5 880 | 8 140 | 9 050 | 10 400 | 11 310 |
| Ø 500 mm | 7 070 | 9 190 | 12 720 | 14 140 | 16 260 | 17 670 |
| Ø 630 mm | 11 220 | 14 590 | 20 200 | 22 440 | 25 810 | 28 060 |
| Ø 800 mm | 18 100 | 23 520 | 32 570 | 36 190 | 41 620 | 45 240 |
| Ø 1000 mm | 28 270 | 36 760 | 50 890 | 56 550 | 65 030 | 70 690 |
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