Rectangular and Circular HVAC Ducts - Equivalent Diameter
Equivalent diameters for rectangular and circular ducts - air flows between 100 - 50,000 cfm
Sponsored Links
The table below can be used to compare equivalent diameters for rectangular and round circular ducts. The table is based on the ducts friction loss formula.
The rectangular dimensions and the air flow volume are adapted to the equal friction loss method of sizing ventilation duct systems. An approximate friction loss of 0.8 inches water gauge per 100 ft duct (6.6 Pa/m) is used.
| Air flow - q - (Cubic Feet per Minute, cfm) (m3/s) |
Rectangular Duct Sizes (Inches) |
Equivalent Diameter Round Duct Sizes - de - (Inches) |
Velocity - v - (ft/min) (m/s) |
Friction Loss (Inches water gauge per 100 ft duct) |
| 200 (0.09) |
3 x 7 4 x 5 |
4.9 4.9 |
1527 (7.8) |
0.88 |
| 300 (0.14) |
4 x 7 5 x 6 |
5.7 6.0 |
1635 (8.3) |
0.82 |
| 400 (0.19) |
4 x 9 5 x 7 6 x 6 |
6.4 6.4 6.6 |
1736 (8.8) |
0.80 |
| 500 (0.24) |
6 x 7 | 7.1 | 1819 (9.2) |
0.78 |
| 750 (0.35) |
5 x 12 6 x 10 7 x 8 |
8.3 8.4 8.2 |
1996 (10.1) |
0.77 |
| 1000 (0.47) |
7 x 10 8 x 9 |
9.1 9.3 |
2166 (11) |
0.79 |
| 1250 (0.59) |
8 x 10 9 x 9 |
9.8 9.8 |
2386 (12.1) |
0.88 |
| 1500 (0.71) |
8 x 12 10 x 10 |
10.7 10.9 |
2358 (11.9) |
0.77 |
| 1750 (0.83) |
8 x 14 9 x 12 10 x 11 |
11.5 11.3 11.5 |
2469 (12.5) |
0.78 |
| 2000 (0.94) |
8 x 15 10 x 12 |
11.8 12.0 |
2589 (13.2) |
0.81 |
| 2500 (1.2) |
10 x 14 12 x 12 |
12.9 13.1 |
2712 (13.8) |
0.8 |
| 3000 (1.4) |
12 x 14 | 14.1 | 2767 (14.1) |
0.75 |
| 3500 (1.7) |
12 x 15 | 14.6 | 3010 (15.3) |
0.84 |
| 4000 (1.9) |
10 x 22 14 x 15 |
15.9 15.8 |
2938 (14.9) |
0.73 |
| 4500 (2.1) |
12 x 19 14 x 16 |
16.4 16.4 |
3068 (15.6) |
0.76 |
| 5000 (2.4) |
10 x 25 12 x 20 15 x 16 |
16.9 16.8 16.9 |
3248 (16.5) |
0.82 |
| 6000 (2.8) |
14 x 20 15 x 18 |
18.2 17.9 |
3358 (17.1) |
0.8 |
| 7000 (3.3) |
12 x 26 16 x 20 |
19.0 19.5 |
3482 (17.7) |
0.8 |
| 8000 (3.8) |
12 x 30 14 x 25 |
20.2 20.2 |
3595 (18.3) |
0.8 |
| 9000 (4.3) |
12 x 34 15 x 25 |
21.4 21.0 |
3671 (18.6) |
0.78 |
| 10000 (4.7) |
12 x 36 16 x 25 20 x 20 |
21.9 21.7 21.9 |
3858 (19.6) |
0.83 |
| 12500 (5.9) |
12 x 45 16 x 30 20 x 24 |
24.1 23.7 23.9 |
4012 (20.4) |
0.8 |
| 15000 (7.1) |
16 x 36 18 x 30 23 x 25 |
24.7 25.2 26.2 |
4331 (22) |
0.87 |
| 17500 (8.3) |
16 x 40 20 x 32 25 x 25 |
27.0 27.5 27.3 |
4337 (22) |
0.79 |
| 20000 (9.4) |
20 x 35 25 x 28 |
28.6 28.9 |
4483 (22.8) |
0.79 |
| 25000 (11.8) |
16 x 55 20 x 43 25 x 38 |
31.0 31.5 33.5 |
4709 (23.9) |
0.78 |
| 30000 (14.2) |
20 x 50 30 x 32 |
33.7 33.9 |
4815 (24.5) |
0.74 |
| 35000 (16.5) |
20 x 55 30 x 35 |
35.2 35.4 |
5179 (26.3) |
0.81 |
| 40000 (18.9) |
25 x 48 30 x 40 |
37.4 37.8 |
5243 (26.6) |
0.77 |
| 45000 (21.2) |
32 x 40 | 39.1 | 5397 (27.4) |
0.77 |
| 50000 (23.6) |
32 x 45 35 x 40 |
41.3 40.9 |
5222 (26.5) |
0.66 |
Sponsored Links
Sponsored Links
Engineering ToolBox - SketchUp Edition - Online 3D modeling!
Engineering ToolBox - SketchUp Edition - enabled for use with the amazing, fun and free Google SketchUp.
Search the ToolBox
© The Engineering ToolBox 2005
9 6 19
