Guideline to Sizing Pipe & Tube

Pipe and tube fittings are sized by the size of the pipe or tube which they mate to, not the size of a feature on the fitting.  For example, you wouldn't measure the face where the gasket seals on tri-clamp fitting or the size of the nut for a bevel seat fitting.

First, measure the outside diameter (O.D.) of the pipe or tube you are trying to find a fitting for.  You might find a ruler doesn't provide enough accuracy.  If so, you might need to use a set of vernier or dial calipers.



If you get a nominal number like 2.00", 3.00", 4.00", etc., you are dealing with tubing.  If you get a number other than nominal such as 1.90" or 2.875" you are dealing with piping.  To find out what size pipe you have, consult the chart below. 

If you want to determine the schedule (thickness) of your pipe, pull out your calculator and apply this formula:

wall thickness = ( O.D. - I.D. ) / 2

Find the outside diameter and wall thickness on the chart below, then read upwards to determine the schedule of the pipe. For example, if your outside diameter was 2.375" and your wall thickness was 0.203", you would have "2 inch schedule 40 pipe" which could also be written as 2" SCH 40 Pipe.

  PIPE SCHEDULE
PIPE SIZES  O.D. (IN)  5 10s  10 40s & Std  40 80s & E.H.  80
Number indicates the wall thickness in inches
0.035 0.049 0.049 0.068 0.068 0.095 0.095
  1/8 0.405 0.049 0.065 0.065 0.088 0.088 0.119 0.119
  1/4 0.540 0.049 0.065 0.065 0.091 0.091 0.126 0.126
  3/8 0.675 0.065 0.083 0.083 0.109 0.109 0.147 0.147
  1/2 0.840 0.065 0.083 0.083 0.113 0.113 0.154 0.154
  3/4 1.050 0.065 0.109 0.109 0.133 0.133 0.179 0.179
1 1.315 0.065 0.109 0.109 0.140 0.140 0.191 0.191
1 1/4 1.660 0.065 0.109 0.109 0.145 0.145 0.200 0.200
1 1/2 1.900 0.065 0.109 0.109 0.154 0.154 0.218 0.218
2 2.375 0.083 0.120 0.120 0.203 0.203 0.276 0.276
2 1/2 2.875 0.083 0.120 0.120 0.216 0.216 0.300 0.300
3 3.50 0.083 0.120 0.120 0.226 0.226 0.318 0.318
3 1/2 4.00 0.083 0.120 0.120 0.237 0.273 0.337 0.337
4 4.50 0.109 0.134 0.134 0.258 0.258 0.375 0.375
5 5.563 0.109 0.134 0.134 0.280 0.280 0.432 0.432
6 6.625 0.109 0.148 0.148 0.322 0.322 0.500 0.500
8 8.625 0.134 0.165 0.165 0.365 0.365 0.500 0.593
10 10.75 0.165 0.180 0.180 0.375 0.406 0.500 0.687
12 12.75   0.188 0.250 0.375 0.437 0.500 0.750
14 14.0   0.188 0.250 0.375 0.500 0.500 0.843
16 16.0   0.188 0.250 0.375 0.562 0.500 0.937
18 18.0   0.218 0.250 0.375 0.593 0.500 1.031
20 20.0   0.250 0.250 0.375 0.687 0.500 1.218
24 24.0   0.250 0.250 0.375 0.687 0.500 1.218