# How to Calculate Wall Size Based on OD and ID

The thickness of a pipe wall depends on its purpose and the materials from which it is constructed.

The outside of a pipe is always larger than the inside. The difference between the inside diameter, or ID, and the outside diameter, or OD, is caused by the thickness of the walls. By calculating the difference between the inside diameter and the outside diameter it is possible to determine the size, or thickness, of the pipe walls. The process uses basic math and requires no previous plumbing experience or knowledge of pipe work.

## Step 1

Subtract the inside diameter from the outside diameter of the pipe. The result is the combined thickness of the pipe walls on both sides of the pipe. For example, if the outside diameter is 6 inches and the inside diameter is 5 inches, the combined size of the opposite pipe walls is 1 inch.

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## Step 2

Divide the total pipe wall thickness by two. The result is the size, or thickness, of one pipe wall. For example, if the total width of both walls is 1 inch, the size of one wall is 1/2 inch -- 1/2 = 1/2.