Here's an equation I used for d9pTo calculate the size of the finished block you need to multiply the size of your original squares by three,
divide by two, then take off one. This will be the finished size of the block.
For example if you begin with 5-inch squares the calculation would be as follows.
5 x 3 = 15, ÷ 2 = 7½ - 1 = 6½ inches.
6-inch squares would yield 8-inch blocks
7-inch squares would yield 9½- inch blocks