Some tips to figure out how big your quilt will be and whether the strips are vertical or horizontal.
Here are the 3 quilts tops I made in one collage photo.
Measure the length of all of your strips sewn together and divide it by 32 (the number of strips in one direction on every quilt). This will give you the measurement in the other direction after sewing 5 seams. The 32 needs to be multiplied by the finished width of your strips (2.5" = 2", 3" = 2.5")
Here are some average sizes if you pieced it Random Plank (straight joining seam) like I did. If you want to do the original diagonal seam shown on the video, it will be a little smaller.
2.5" strips--- If the number in the left column is smaller than the one in the right column, the strips are horizontal. When the left column number is larger the strips will be vertical or lengthwise on the quilt.
40 strips = 52.5" x 64"
50 strips = 65.5" x 64"
55 strips = 72" x 64"
60 strips = 78.5" x 64"
65 strips = 85" x 64"
70 strips = 91.5" x 64"
3" strips
40 strips = 52.5" x 80"
50 strips = 65.5" x 80"
60 strips = 78.5" x 80"
70 strips = 92" x 80"
80 strips = 105" x 80"
Disclaimer: I am only human, I hope I didn't make any errors, and the numbers above are approximate. Mine came out a little narrower than planned because my seam was a touch wider than 1/4".