Formula for figuring your front and back sashings. (This is only if you are using the folding method. )
[ Final width of Sashing ] + [ 1/2"] = Width of top Sashing.
[ Final width of Top Sashing * 2 ] + [ 3/4"] = Width to cut back Sashing.
EXAMPLE using the formula.
Front Sashing > [The Final Width of my Sashing will be 4 inches.] + [1/2"] = 4- 1/2" width
Back Sashing > [ 4" x 2] + [ 3/4" ] = 8- 3/4" width
Hope this helps clarify a bit more.