? about car/truck exhaust

[BIGCRIP28]

How do you measure what size exhaust pipe you have?
I used a micrometer and measure the out side and it is 2.25".
When people say I have 3", 5" this means out side diameter right?
So I have a 2 1/4" then.

Does this mean I need an 2.25" or 2.5" inlet muffler?
Some people on ebay measure the outside and some measure the inside of the inlet.
I thought 2.25" inlet meant that a 2.25" pipe would slip in there and you could clamp it on.

[84honda 200X]

The way i do it is i measure the diameter of the pipe with a tape measure. Like from one side to the other when its not put together. You could use 2 and a quarter but it would be the same size as the 2 and a fourth so you would have to butt weld them together. I would use a 2.5 inlet muffler it should just slip over the pipe.