The calculator below is based on formula (1). The formula is generic and any unit can be used.
Equivalent diameters for some common mm rectangular duct dimensions:
For full table with larger dimensions - rotate the screen!
Circular equivalent diameter - de (mm) | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Duct side - a - (mm) | Duct side - b (mm) | ||||||||||||||
100 | 150 | 200 | 250 | 300 | 400 | 500 | 600 | 800 | 1000 | 1200 | 1400 | 1600 | 1800 | 2000 | |
100 | 109 | 133 | 152 | 168 | 183 | 207 | 227 | ||||||||
150 | 133 | 164 | 189 | 210 | 229 | 261 | 287 | 310 | |||||||
200 | 152 | 189 | 219 | 244 | 266 | 305 | 337 | 365 | |||||||
250 | 168 | 210 | 246 | 273 | 299 | 343 | 381 | 414 | 470 | ||||||
300 | 183 | 229 | 266 | 299 | 328 | 378 | 420 | 457 | 520 | 574 | |||||
400 | 207 | 260 | 305 | 343 | 378 | 437 | 488 | 531 | 609 | 674 | 731 | ||||
500 | 227 | 287 | 337 | 381 | 420 | 488 | 547 | 598 | 687 | 762 | 827 | 886 | |||
600 | 310 | 365 | 414 | 457 | 531 | 598 | 656 | 755 | 840 | 914 | 980 | 1041 | |||
800 | 414 | 470 | 520 | 609 | 687 | 755 | 875 | 976 | 1066 | 1146 | 1219 | 1286 | |||
1000 | 517 | 574 | 674 | 762 | 840 | 976 | 1093 | 1196 | 1289 | 1373 | 1451 | 1523 | |||
1200 | 620 | 731 | 827 | 914 | 1066 | 1196 | 1312 | 1416 | 1511 | 1598 | 1680 | ||||
1400 | 781 | 886 | 980 | 1146 | 1289 | 1416 | 1530 | 1635 | 1732 | 1822 | |||||
1600 | 939 | 1041 | 1219 | 1373 | 1511 | 1635 | 1749 | 1854 | 1952 | ||||||
1800 | 1096 | 1286 | 1451 | 1598 | 1732 | 1854 | 1968 | 2073 | |||||||
2000 | 1523 | 1680 | 1822 | 1952 | 2073 | 2186 |
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Equivalent diameters of some common inches rectangular ducts:
For full table - rotate the screen!
Circular equivalent diameter (inches) | |||||||
---|---|---|---|---|---|---|---|
Length - b - (inches) | Length - a - (inches) | ||||||
4 | 5 | 6 | 8 | 10 | 12 | 16 | |
4 | 4.4 | 4.9 | 5.3 | 6.1 | |||
5 | 4.9 | 5.5 | 6 | 6.9 | 7.6 | ||
6 | 5.3 | 6 | 6.6 | 7.6 | 8.4 | 9.1 | |
8 | 6.1 | 6.9 | 7.6 | 8.6 | 9.8 | 10.7 | 12.2 |
10 | 7.6 | 8.4 | 9.8 | 10.9 | 12 | 13.7 | |
12 | 9.1 | 10.7 | 12 | 13.1 | 15.1 | ||
16 | 12.2 | 13.7 | 15.1 | 17.5 |
print equivalent diameter diagram!
Flat oval ducts have smaller height requirements than round ducts and retain most of the advantages of the round ducts. Fittings for flat oval ducts are difficult to fabricate or modify in the field.
The equivalent diameter of a oval duct or tube (ellipse) can be calculated as (Heyt & Diaz)
de = 1.55 A0.625 / P0.25 (2)
where
A = cross-sectional area oval duct (m2, in2)
P = perimeter oval duct (m, inches)
The cross-sectional area of an oval duct can be expressed as
A = π a b / 4
where
a = major dimension of the flat oval duct (m, in)
b = minor dimension of the flat oval duct (m, in)
The perimeter of an oval duct (ellipse) can be approximated to
P ≈ 2 π (1/2 ((a / 2)2 + (b / 2)2))1/2 (2b)
Equivalent diameters of oblong ducts or pipes can be expressed as
de = 1.55 (π b2 / 4 + a b - b2)0.625/(π b + 2 a - 2 b)0.25 (3)
Note! - equivalent diameter is not the same as hydraulic diameter. The hydraulic diameter express the rate between the area section of the duct or tube, and the wetted perimeter of the duct or tube. Hydraulic diameter is used to determine if the flow is laminar or turbulent and to calculate the pressure loss.
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