Currently in the process of sewing a GFG. You need to know three things:
If you are doing a center plus one round of petals, you need 12 path hexagons for the first block. Because subsequent blocks share path hexagons with the first block and each other, fewer are required. I would make 8. Your total no of hexes is (No of blocks * 8) + 4.
If you are doing two rounds of petals, you need 18 path hexagons for the first block. I would count 12 for subsequent blocks. So your total hexes are (No of blocks * 12) + 6.
How big a patch do you need to cut each hexagon? I cut mine with flat side on the top and bottom. So I measure top to bottom of a finished hex, add 1/2”. To see how many hexes you get out of a strip, measure point to point on a finished hex and add 1/2”
Now figure out how many you can cut from a strip. My patches are 3.5 x 4.5, so i get 8 from each strip.
Divide the total you need by how many you get out of each strip and round up. Multiply by strip width, 9 (for the inevitable crooked cuts) and divide that total by 36. Round up to the nearest 1/8 yard. Buy that much and hope it