Are you talking about a postage stamp quilt with 2.5" squares only?
If so........1 hopefully
Now I have made quite a few quilts with my 2 1/2" squares. They go faster since they are accompanied with larger size pieces.
I do use my squares as leaders and enders so every once in awhile I will make a 4 squares x 4 squares blocks. I probably have 20 of those made...... I guess that is a start of a postage stamp quilt.
Good luck
Tell us what you decide