I need 3" x 2.5", 56 pieces, what size piece of steel would I need with the least amount of waste?
OK. I hope this wasn't a math homework problem or something because I can't really describe the process I used other than creative trial and error, but if you cut 28 squares from 2 larger sheets of steel 6" x 36" in size, you will only have 12 in.2 of waste at the end of all the cutting. I couldn't really find a one-sheet solution with the dimensions you gave that didn't waste a whole lot of steel, but if you do it this way, I think you'll be alright. I'll try to explain the layout:
Picture two rows of these tinier pieces with their 3" edges lined up against the 6" width of the larger sheet. With this layout, you can fit 14 of these tinier pieces (with their 2.5" dimension) into 35" - just 1" short of the 36" length of the larger sheet. So, out of one sheet, you've got half of your tiny pieces with just 6 in.2 of waste. Do this with another large sheet of steel with the same dimensions, and you'll have the other half of your pieces with only another 6 in.2 of waste for a total of only 12 in.2 of waste.
Hope this helps!