Exhaust inside / outside diamter

[civicx3]

Finding different info online as usual and seems some manufactures do things differently

When talking about a exhaust system thats 2.5", 3" etc.. is this the outside diameter or inside?

Using this as a example, are they using id or od here..?

 

[rvm]

Depends on the brand, but most "famous' brands offer the exahust systems measuring their inside diameter

 

[Eoghain]

Most pipe diameters specify the OD and the ID is a function of that according to a specific standard. Tube can can come specifying the ID. According to engineering standards pipe and tube are two "different" types of profiles. It's far more common to buy material based on the OD hence why most exhaust manufactures quote pipe OD. The cost difference between 3.0 inch OD compared to 3.0 inch ID could be a factor of 10!

looking at the pipe area quoted for the 3.0 inch pipe in that table I'd say they are quoting OD as the pipe diameter

 

[civicx3]

yeah ive read pipe and tube can be classed as different which makes no sense to me. From what ive seen most use OD so a 2.5" exhaust is actually smaller than 2.5" ID

but like rvm says some use ID so you would be buying a bigger exhaust even tho its being branded the same diameter, confusing!

 

[Murray]

Tube is measured by outside diameter, pipe is measured by inside diameter.