I want to end up with a 2 1/2" HST what size do I cut the strips to end up with that size?

Usually you would add 7/8" but I prefer to cut 1" extra so that would be 3 1/2" square, sew on the diagonal, cut and trim. Let me know if you need directions.

Are you using the stitching a quarter of an inch from the diagonal line method? If so,cut your strips into 3" squares, make your HSTs and then trim to size, assuming your 2.5" is the unfinished size.

Yes I am drawing a line diagonally and then sewing 1/4 on either size and then cutting on the line. I thought that was right but needed confirmation Thanks so much!