Not necessarily. It really depends on how many pieces you can get out of one strip of fabric. For example:
size of finished item: 60"x60"
size of finished HST: 4" (2 squares cut at 4 7/8" will yield 2 HSTs--round up to 5" for easier calculation)
amount of HSTs needed: 175 (60"divided by 4"=15 wide x 15 long)
amount of squares needed: 88 of each colour (one square of each colour will yield 2 HSTs)
With me so far?
If we figure that your fabric has 40" useable width, and that you are cutting 5" squares, you can get 8 squares per strip 5" strip of fabric. Because you need 88 squares, you need 11 strips of fabric (total needed divided by amount per strip). Therefore, you would need 55" of each fabric.
BUT if you made those HSTs 6" finished, you would then have to cut your squares at 7". So lets do the same math. 60"x60" divided by 6" =100 finished blocks which means you would need 50 of each colour. But you would only be able to get 5 squares out of each strip of fabric. (40 divided by 7) which means that you would need 10 strips and that would equal 70" of each colour.
It really comes down to how many squares you can cut from your useable width of fabric. Sometimes bigger is not more economical.