Am I the only one who didn't know this??
 

For the first time I bought a jelly roll. This was described as 42 pcs of 2-1/2" strips. Well I started working and my 2-1/2" squares didn't match up to the jelly roll. The jelly roll is actually 2-3/4" wide. Not sure maybe it is 2-1/2" from the "ditch" of the pinking cut. Is that how all jelly rolls are?

If anything, I've found rolls to be a skimpy 2.5" Is it possible you subcut the 2.5" strip into 2.75" units (i.e. 2.5 x 2.75")?

I don't think they are all that way, at least yours is 1/4 inch bigger than 1/4 inch to small!
I have always heard you use the outside edge of the pinking as your seam guide.

well I am 100% positive that I measured the strip.. from pinked edge to pinked edge. At least now I know to check before I start my next project Yes I agree.... bigger is better than smaller!!

What brand?

I never have had an issue with precuts being mis-sized, with the exception of one fabric manufacturer. They were pretty bad.

I just made a trip around the world quilt using strips from several different jelly roll packs. Silly me, I didn't think to measure first. I ended up having to do some extra work making everything fit because some were as much as 1/4 inch off. I like jelly rolls in general because you get a bunch of different colors that all go together, but won't be doing another project mixing strips from different rolls without measuring first!

I gave up on pre-cuts not long after they came out. They weren't worth the trouble to me.

I found that Moda pre cuts have always been perfectly cut to size for me. Some other brands are not. Moda will replace any precut that are off in size.

I also found out the hard way that the jelly roll wasn't the right size when I matched it up with precut strips from stash. Now I make sure to premeasure (if I buy a precut at all).

I have only worked with one jelly roll and they were all the same size. I cut some strips from my stash to go with them and had no problems. The jelly roll was a gift from my Daughter. I have too much fabric to buy any precuts.