ANSI Flange Measurements and Ratings

How to measure a pump flange

ANSI flanges generally follow standard measurements. If you order just a single flange from one company, it's measurements should very closely match that of another company. While this is true for individual flanges, it is not true for pumps. Pump casings are often designed to bolt to a ANSI flange, with similar pressure ratings of the ANSI flange. However, these flanges often do not follow all of the ANSI standard measurements.

When trying to determine the flange rating of a pump, the best method is to look for a stamp printed onto the flange. If one is not visible, or it is worn, then start by counting the number of bolt holes. This will point you to a narrower range of flange sizes in the chart below. Next measure the bolt circle diameter. In most cases, these two pieces of information is enough to determine the flange size from the charts.

If these measurements do not single out a flange, measure the bolt hole diameter. You can also double check the flange size by measuring the inner diameter of the pipe when available. The inner diameter may not be exact, but within a 1/8 inch. Not all flange sizes have a standard inner diameter and therefore are not included in the table below.

 

Bolt Holes Bolt Circle Bolt Hole Diameter Pipe I.D. Flange Size Flange Rating Pressure Rating*
4 3 1/8" 5/8" 1.05" 1" 150# 285 PSI
4 3 1/2" 5/8" 1.375" 1 1/4" 150# 285 PSI
4 3 1/2" 3/4" 1.05" 1" 300# 740 PSI
4 3 1/2" 3/4"   1" 600# 1480 PSI
4 3 7/8" 5/8" 1.61" 1 1/2" 150# 285 PSI
4 3 7/8" 3/4" 1.38" 1 1/4" 300# 740 PSI
4 3 7/8" 3/4"   1 1/4" 600# 1480 PSI
4 4" 1"   1" 1500# 3705 PSI
4 4" 1"   1" 900# 2220 PSI
4 4 3/8" 1"   1 1/4" 1500# 3705 PSI
4 4 3/8" 1"   1 1/4" 900# 2220 PSI
4 4 1/2" 7/8" 1.61 1 1/2" 300# 740 PSI
4 4 1/2" 7/8"   1 1/2" 600# 1480 PSI
4 4 1/2" 1"   1" 2500# 6170 PSI
4 4 3/4" 3/4" 2.07" 2" 150# 285 PSI
4 4 7/8" 1 1/8"   1 1/2" 1500# 3705 PSI
4 4 7/8" 1 1/8"   1 1/2" 900# 2220 PSI
4 5 1/8" 1 1/8"   1 1/4" 2500# 6170 PSI
4 5 1/2" 3/4" 2.47" 2 1/2" 150# 285 PSI
4 5 3/4" 1 1/4"   1 1/2" 2500# 6170 PSI
4 6" 3/4" 3.07" 3" 150# 285 PSI
8 5" 3/4" 2.07" 2" 300# 740 PSI
8 5" 3/4"   2" 600# 1480 PSI
8 5 7/8" 7/8" 2.47" 2 1/2" 300# 740 PSI
8 5 7/8" 7/8"   2 1/2" 600# 1480 PSI
8 6 1/2" 1"   2" 1500# 3705 PSI
8 6 1/2" 1"   2" 900# 2220 PSI
8 6 5/8" 7/8" 3.07" 3" 300# 740 PSI
8 6 5/8" 7/8"   3" 600# 1480 PSI
8 6 3/4" 1 1/8"   2" 2500# 6170 PSI
8 7" 3/4" 3.55" 3 1/2" 150# 285 PSI
8 7 1/4" 7/8" 3.55" 3 1/2" 300# 740 PSI
8 7 1/4" 1"   3 1/2" 600# 1480 PSI
8 7 1/2" 3/4" 4.03" 4" 150# 285 PSI
8 7 1/2" 1"   3" 900# 2220 PSI
8 7 1/2" 1 1/8"   2 1/2" 1500# 3705 PSI
8 7 1/2" 1 1/8"   2 1/2" 900# 2220 PSI
8 7 3/4" 1 1/4"   2 1/2" 2500# 6170 PSI
8 7 7/8" 7/8" 4.03" 4" 300# 740 PSI
8 8" 1 1/4"   3" 1500# 3705 PSI
8 8 1/2" 7/8" 5.05" 5" 150# 285 PSI
8 8 1/2" 1"   4" 600# 1480 PSI
8 9" 1 3/8"   3" 2500# 6170 PSI
8 9 1/4" 7/8" 5.05" 5" 300# 740 PSI
8 9 1/4" 1 1/4"   4" 900# 2220 PSI
8 9 1/2" 7/8" 6.07" 6" 150# 285 PSI
8 9 1/2" 1 3/8"   4" 1500# 3705 PSI
8 10 1/2" 1 1/8"   5" 600# 1480 PSI
8 10 3/4" 1 5/8"   4" 2500# 6170 PSI
8 11" 1 3/8"   5" 900# 2220 PSI
8 11 1/2" 1 1/2"   5" 1500# 3705 PSI
8 11 3/4" 7/8" 7.98" 8" 150# 285 PSI
8 12 3/4" 1 7/8"   5" 2500# 6170 PSI
8 14 1/2" 2 1/8"   6" 2500# 6170 PSI
12 10 5/8" 7/8" 6.07" 6" 300# 740 PSI
12 11 1/2" 1 1/8"   6" 600# 1480 PSI
12 12 1/2" 1 1/4"   6" 900# 2220 PSI
12 12 1/2" 1 1/2"   6" 1500# 3705 PSI
12 13" 7/8" 7.98" 8" 300# 740 PSI
12 13 3/4" 1 1/8"   8" 600# 1480 PSI
12 14 1/4" 1" 10.02" 10" 150# 285 PSI
12 15 1/2" 1 3/8"   8" 900# 2220 PSI
12 15 1/2" 1 5/8"   8" 1500# 3705 PSI
12 17" 7/8" 12" 12" 150# 285 PSI
12 17 1/4" 2"   8" 2500# 6170 PSI
12 19" 2"   10" 1500# 3705 PSI
12 21 1/4" 2 5/8"   10" 2500# 6170 PSI
12 24 3/8" 2 3/4"   12" 2500# 6170 PSI
16 15 1/4" 1 1/8" 10.02" 10" 300# 740 PSI
16 17" 1 3/8"   10" 600# 1480 PSI
16 17 3/4" 1 1/8" 12.00" 12" 300# 740 PSI
16 18 1/2" 1 1/2"   10" 900# 2220 PSI
16 22 1/2" 2"   12" 1500# 6170 PSI
20 19 1/4" 1 1/4"   12" 600# 1480 PSI
20 21" 1 3/8"   12" 900# 2220 PSI

*Pump manufacturers will sometimes change the flange on a pump's inlet or outlet. Although the pressure rating of the flange changes, the rating of the pump itself does not change. Do not attempt to pressure a pump beyond the maximum allowable pressure found on the pump nameplate or withing the user manual. Doing so may result in damage to equipment or danger to operators.