For an example - say you want to make a top that is 72 x 72 inches - the reason for choosing that number is that 72 is evenly divisibly by 8, 6, 4, and 2.
The area of the finished top would be 72 x 72 = 5184 square inches
THE FOLLOWING IS THEORETICAL WITH NO WASTE, NO SHRINKAGE, AND NO ALLOWANCE FOR FABRIC WIDTH - JUST SQUARE INCHES OF FABRIC NEEDED
If one wanted to make a top of 8 inch HST units -
72 divided by 8 = 9
So there would be 9 x 9 (81) HST units in a top made of 8 inch (finished size) units
Each HST would theoretically take 8.875 x 8.875 (78.77) square inches of fabric
Multiply the number of units times the number of square inches for each unit
81 x 78.77 = 6380.02 square inches
For 6 inch finished units
72/6 x 72/6 x 6.875 x 6.875 = 6806.25 square inches
for 4 inch finished units
72/4 x 72/4 x 4.875 x 4.875 = 7700.07 square inches
for 2 inch finished HST units
72/2 x 72/x x 2.875 x 2.875 = 10712.25
The process is:
A. Divide finished length by finished size
B. Divide finished width by finished size
C. Multiply A x B to get the number of units needed
D. Multiply the size of the square needed to make a HST x C - be sure to multiply length x width for the area needed.
I think my numbers are correct - but if not - please update them.