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Rectangular Ducts - Hydraulic Diameter

Calculate hydraulic diameter for rectangular ducts - metric units.

Hydraulic diameter for rectangular ducts can be calculated as

d_h = 2 a b / (a + b) (1)

where

d_h = hydraulic diameter (mm, in)

a = width of the duct (mm, in)

b = height of the duct (mm, in)

Hydraulic diameter of some common rectangular ducts:

Rectangular Ducts - Hydraulic Diameters
Width of Duct (mm)	Hydraulic Diameter - d_h - (mm)
	Height of Duct (mm)
	100	150	200	250	300	400	500	600	800	1000	1200
200	133	171	200
250	143	188	122	250
300	150	200	222	273	300
400	160	218	240	308	343	400
500		231	267	333	375	444	500
600		240	286	353	400	480	545	600
800			300	381	436	533	615	686	800
1000			320	400	462	571	667	750	889	1000
1200					480	600	706	800	960	1091	1200
1400						622	737	840	1018	1167	1292
1600						640	762	873	1067	1231	1371
1800							783	900	1108	1286	1440
2000							800	923	1143	1333	1500