Rectangular and Round Duct Sizes Chart - A Field Duct Sizing

Rectangular Duct Sizes Chart

Duct Size(cfm)4″
606×4
908×4
12010×4
15012×4
18014×4
21016×4
24018×4
27020×4
30022×4
33024×4
4021/2×10
7021/2×14
15021/2×30
Duct Size(cfm)6″
604×6
1106×6
1608×6
21510×6
27012×6
32014×6
37516×6
43018×6
49020×6
54022×6
60024×6
65026×6
71028×6
77530×6
10031/2×14
22031/2×30
Duct Size(cfm)8″
904×8
1606×8
2308×8
31010×8
40012×8
49014×8
58016×8
67018×8
75020×8
84022×8
93024×8
102026×8
110028×8
120030×8
130032×8
140034×8
150036×8
Duct Size(cfm)10″
1204×10
2156×10
3108×10
43010×10
55012×10
67014×10
80016×10
93018×10
106020×10
120022×10
132024×10
143026×10
155028×10
167030×10
180032×10
193034×10
206036×10
220038×10
235040×10
Duct Size(cfm)12″
1504×12
2706×12
4008×12
55010×12
68012×12
80014×12
95016×12
110018×12
125020×12
140022×12
160024×12
175026×12
195028×12
215030×12
230032×12
245034×12
260036×12
275038×12
290040×12
305042×12
Rectangular Sheet Metal Duct = .07″ on most metal duct calculations

Round Duct Sizes Chart

Flexible Duct
Duct SizeDesign Airflow
5″50
6″75
7″110
8″160
9″225
10″300
12″480
14″700
16″1000
18″1300
20″1700
Flex Duct = .05″ on most metal duct calculations
Round Metal Pipe
Duct SizeDesign Airflow
5″50
6″85
7″125
8″180
9″240
10″325
12″525
14″750
16″1200
18″1500
20″2000
Round Metal Pipe = .06″ on most metal duct calculations