ANSI Flange PCDs and Dimensions

Flange dimensions are determined by pipe size and pressure class required for the application. These dimensions have been standardised and published by bodies such as The American National Standards Institute (ANSI).
 

ANSI B16.5. Flange PCD Dimensions

Dimensions for pitch circle diameter (PCD) of flange bolts, and the bolt sizes for the most common pipe sizes and flange ratings are shown in the tables below.
 
- All bolt holes are 1/8" larger than diameter of bolts.
See our page on Stud and Nut Sizes to determine the correct nut size.
 

ANSI 150#
Pipe NB	Bolt PCD	No. of Bolts	Bolt Size	Flange OD
1/2"	2 3/8"	4	1/2"	3 1/2"
1"	3 1/8"	4	1/2"	4 1/4"
2"	4 3/4"	4	5/8"	6"
4"	7 1/2"	8	5/8"	9"
6"	9 1/2"	8	3/4"	11"
8"	11 3/4"	8	3/4"	13 1/2"
10"	14 1/4"	12	7/8"	16"
12"	17 "	12	7/8"	19"
14"	18 3/4"	12	1"	21"

 

ANSI 300#
Pipe NB	Bolt PCD	No. of Bolts	Bolt Size	Flange OD
1/2"	2 5/8"	4	1/2"	3 3/4"
1"	3 1/2"	4	5/8"	4 7/8"
2"	5"	8	5/8"	6 1/2"
4"	7 7/8"	8	3/4"	10"
6"	10 5/8"	12	3/4"	12 1/2"
8"	13"	12	7/8"	15"
10"	15 1/4"	16	1"	17 1/2"
12"	17 3/4"	16	1 1/8"	20 1/2"
14"	20 1/4"	20	1 1/8"	23"

 

ANSI 600#
Pipe NB	Bolt PCD	No. of Bolts	Bolt Size	Flange OD
1/2"	2 5/8"	4	1/2"	3 3/4"
1"	3 1/2"	4	5/8"	4 7/8"
2"	5"	8	5/8"	6 1/2"
4"	8 1/2"	8	7/8"	10 3/4"
6"	11 1/2"	12	1"	14"
8"	13 3/4"	12	1 1/8"	16 1/2"
10"	17"	16	1 1/4"	20"
12"	19 1/4"	20	1 1/4"	22"
14"	20 3/4"	20	1 3/8"	23 3/4"

 

ANSI 900#
Pipe NB	Bolt PCD	No. of Bolts	Bolt Size	Flange OD
2" *	6 1/2"	8	7/8"	8 1/2"
4"	9 1/4"	8	1 1/8"	11 1/2"
6"	12 1/2"	12	1 1/8"	15"
8"	15 1/2"	12	1 3/8"	18 1/2"
10"	18 1/2"	16	1 3/8"	21 1/2"
12"	21"	20	1 3/8"	24"
14"	22"	20	1 1/2"	25 1/4"
* 2" Class 1500 is used for 2" Class 900

 

ANSI 1500#
Pipe NB	Bolt PCD	No. of Bolts	Bolt Size	Flange OD
2"	6 1/2"	8	7/8"	8 1/2"
4"	9 1/2"	8	1 1/4"	12 1/4"
6"	12 1/2"	12	1 3/8"	15 1/2"
8"	15 1/2"	12	1 5/8"	19"