What is Nominal Pipe Size (NPS)?

Pipe size, or Nominal Pipe Size (NPS), is a North American industry designation, or "trade size", that was standardized by the American Standards Association. The use of the word "nominal" in the NPS designation refers to non-specific terms and identifies the diameter of the hole with a non-dimensional number^[1]. For example, one of the most common pipe sizes to use when fabrication a turbo manifold is 1-1/2" Schedule 10; however, the approximate outside diameter (OD) of this material is 1.900" and the approximate inside diameter (ID) is 1.682". Based on those dimensions it's easy to see that even though the material is referred to as 1-1/2" pipe there isn't a single dimension that is actually 1.500". Due to the nominal sizing of pipe we never list or reference the material on our website as a decimal (e.g., 1.500") like we do with tube size material.

Below is a chart of standard pipe sizes ranging from 1/8" to 4".

Note: Pipe size material is only compatible with other pipe size material (pipe size weld els, tees, reducers, straight lengths, etc). Pipe size material is not compatible with stainless steel tube, tube fittings, or mandrel bends that are sized by the outside diameter.

Note: Please be sure to verify that this item meets the requirements of your project. It is the customer's responsibility to verify the compatibility of the items in their shopping cart. Ace Race Parts is not responsible for orders with mismatched, or incompatible, products.