Duct fitting pressure drop coefficients for
round transition

From ASHRAE (1989), with permission

A5-6f.gif (12064 bytes)

Values for C

q, deg

10

15

20

30

45

60

90

120

150

180

A0 / A1

0.06

0.21

0.29

0.38

0.60

0.84

0.88

0.88

0.88

0.88

0.88

0.1

0.21

0.28

0.38

0.59

0.76

0.80

0.83

0.84

0.83

0.83

0.25

0.16

0.22

0.30

0.46

0.61

0.68

0.64

0.63

0.62

0.62

0.5

0.11

0.13

0.19

0.32

0.33

0.33

0.32

0.31

0.30

0.30

1*

0

0

0

0

0

0

0

0

0

0

2

0.20

0.20

0.20

0.20

0.22

0.24

0.48

0.72

0.96

1.0

4

0.80

0.64

0.64

0.64

0.88

1.1

2.7

4.3

5.6

6.6

6

1.8

1.4

1.4

1.4

2.0

2.5

6.58

10

13

15

10

5.0

5.0

5.0

5.0

6.5

8.0

19

29

31

43

*for equal-area transition from square to round, use C = 0.15.