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Flange dimensions are determined by pipe size and pressure class required for the application.

Most of these dimensions have been standardized and published as ASME, MSS, API or other standardization organization specifications.

ASME/ANSI B16.5 provides dimensions and tolerances for flanges in pipe sizes from 1/2"

through 24" and in classes ranging 150 through 2500.

Nominal Pipe Size
NPS
(inches)		 Class 150
Diameter of
Flange
(inches)		 No.
of
Bolts		 Diameter of
Bolts
(inches)		 Bolt
Circle
(inches)
1/4 3-3/8 4 1/2 2-1/4
1/2 3-1/2 4 1/2 2-3/8
3/4 3-7/8 4 1/2 2-3/4
1 4-1/4 4 1/2 3-1/8
1-1/4 4-5/8 4 1/2 3-1/2
1-1/2 5 4 1/2 3-7/8
2 6 4 5/8 4-3/4
2-1/2 7 4 5/8 5-1/2
3 7-1/2 4 5/8 6
3-1/2 8-1/2 8 5/8 7
4 9 8 5/8 7-1/2
5 10 8 3/4 8-1/2
6 11 8 3/4 9-1/2
8 13-1/2 8 3/4 11-3/4
10 16 12 7/8 14-1/4
12 19 12 7/8 17
14 21 12 1 18-3/4
16 23-1/2 16 1 21-1/4
18 25 16 1-1/8 22-3/4
20 27-1/2 20 1-1/8 25
24 32 20 1-1/4 29-1/2
Nominal Pipe Size
NPS
(inches)		 Class 300
Diameter of
Flange
(inches)		 No.
of
Bolts		 Diameter of
Bolts
(inches)		 Bolt
Circle
(inches)
1/4 3-3/8 4 1/2 2-1/4
1/2 3-3/4 4 1/2 2-5/8
3/4 4-5/8 4 5/8 3-1/4
1 4-7/8 4 5/8 3-1/2
1-1/4 5-1/4 4 5/8 3-7/8
1-1/2 6-1/8 4 3/4 4-1/2
2 6-1/2 8 5/8 5
2-1/2 7-1/2 8 3/4 5-7/8
3 8-1/4 8 3/4 6-5/8
3-1/2 9 8 3/4 7-1/4
4 10 8 3/4 7-7/8
5 11 8 3/4 9-1/4
6 12-1/2 12 3/4 10-5/8
8 15 12 7/8 13
10 17-1/2 16 1 15-1/4
12 20-1/2 16 1-1/8 17-3/4
14 23 20 1-1/8 20-1/4
16 25-1/2 20 1-1/4 22-1/2
18 28 24 1-1/4 24-3/4
20 30-1/2 24 1-1/4 27
24 36 24 1-1/2 32
Nominal Pipe Size
NPS
(inches)		 Class 400
Diameter of
Flange
(inches)		 No.
of
Bolts		 Diameter of
Bolts
(inches)		 Bolt
Circle
(inches)
1/4 3-3/8 4 1/2 2-1/4
1/2 3-3/4 4 1/2 2-5/8
3/4 4-5/8 4 5/8 3-1/4
1 4-7/8 4 5/8 3-1/2
1-1/4 5-1/4 4 5/8 3-7/8
1-1/2 6-1/8 4 3/4 4-1/2
2 6-1/2 8 5/8 5
2-1/2 7-1/2 8 3/4 5-7/8
3 8-1/4 8 3/4 6-5/8
3-1/2 9 8 7/8 7-1/4
4 10 8 7/8 7-7/8
5 11 8 7/8 9-1/4
6 12-1/2 12 7/8 10-5/8
8 15 12 1 13
10 17-1/2 16 1-1/8 15-1/4
12 20-1/2 16 1-1/4 17-3/4
14 23 20 1-1/4 20-1/4
16 25-1/2 20 1-3/8 22-1/2
18 28 24 1-3/8 24-3/4
20 30-1/2 24 1-1/2 27
24 36 24 1-3/4 32
Nominal Pipe Size
NPS
(inches)		 Class 600
Diameter of
Flange
(inches)		 No.
of
Bolts		 Diameter of
Bolts
(inches)		 Bolt
Circle
(inches)
1/4 3-3/8 4 1/2 2-1/4
1/2 3-3/4 4 1/2 2-5/8
3/4 4-5/8 4 5/8 3-1/4
1 4-7/8 4 5/8 3-1/2
1-1/4 5-1/4 4 5/8 3-7/8
1-1/2 6-1/8 4 3/4 4-1/2
2 6-1/2 8 5/8 5
2-1/2 7-1/2 8 3/4 5-7/8
3 8-1/4 8 3/4 6-5/8
3-1/2 9 8 7/8 7-1/4
4 10-3/4 8 7/8 8-1/2
5 13 8 1 10-1/2
6 14 12 1 11-1/2
8 16-1/2 12 1-1/8 13-3/4
10 20 16 1-1/4 17
12 22 20 1-1/4 19-1/4
14 23-3/4 20 1-3/8 20-3/4
16 27 20 1-1/2 23-3/4
18 29-1/4 20 1-5/8 25-3/4
20 32 24 1-5/8 28-1/2
24 37 24 1-7/8 33
Nominal Pipe Size
NPS
(inches)		 Class 900
Diameter of
Flange
(inches)		 No.
of
Bolts		 Diameter of
Bolts
(inches)		 Bolt
Circle
(inches)
1/2 4-3/4 4 3/4 3-1/4
3/4 5-1/8 4 3/4 3-1/2
1 5-7/8 4 7/8 4
1-1/4 6-1/4 4 7/8 4-3/8
1-1/2 7 4 1 4-7/8
2 8-1/2 8 7/8 6-1/2
2-1/2 9-5/8 8 1 7-1/2
3 9-1/2 8 7/8 7-1/2
4 11-1/2 8 1-1/8 9-1/4
5 13-3/4 8 1-1/4 11
6 15 12 1-1/8 12-1/2
8 18-1/2 12 1-3/8 15-1/2
10 21-1/2 16 1-3/8 18-1/2
12 24 20 1-3/8 21
14 25-1/4 20 1-1/2 22
16 27-3/4 20 1-5/8 24-1/2
18 31 20 1-7/8 27
20 33-3/4 20 2 29-1/2
24 41 20 2-1/2 35-1/2
Nominal Pipe Size
NPS
(inches)		 Class 1500
Diameter of
Flange
(inches)		 No.
of
Bolts		 Diameter of
Bolts
(inches)		 Bolt
Circle
(inches)
1/2 4-3/4 4 3/4 3-1/4
3/4 5-1/8 4 3/4 3-1/2
1 5-7/8 4 7/8 4
1-1/4 6-1/4 4 7/8 4-3/8
1-1/2 7 4 1 4-7/8
2 8-1/2 8 7/8 6-1/2
2-1/2 9-5/8 8 1 7-1/2
3 10-1/2 8 1-1/8 8
4 12-1/4 8 1-1/4 9-1/2
5 14-3/4 8 1-1/2 11-1/2
6 15-1/2 12 1-3/8 12-1/2
8 19 12 1-5/8 15-1/2
10 23 12 1-7/8 19
12 26-1/2 16 2 22-1/2
14 29-1/2 16 2-1/4 25
16 32-1/2 16 2-1/2 27-3/4
18 36 16 2-3/4 30-1/2
20 38-3/4 16 3 32-3/4
24 46 16 3-1/2 39
Nominal Pipe Size
NPS
(inches)		 Class 2500
Diameter of
Flange
(inches)		 No.
of
Bolts		 Diameter of
Bolts
(inches)		 Bolt
Circle
(inches)
1/2 5-1/4 4 3/4 3-1/2
3/4 5-1/2 4 3/4 3-3/4
1 6-1/4 4 7/8 4-1/4
1-1/4 7-1/4 4 1 5-1/8
1-1/2 8 4 1-1/8 5-3/4
2 9-1/4 8 1 6-3/4
2-1/2 10-1/2 8 1-1/8 7-3/4
3 12 8 1-1/4 9
4 14 8 1-1/2 10-3/4
5 16-1/2 8 1-3/4 12-3/4
6 19 8 2 14-1/2
8 21-3/4 12 2 17-1/4
10 26-1/2 12 2-1/2 21-1/4
12 30 12 2-3/4 24-3/8