Most of Matt's box pleated kilts have 7-9 pleats. I'm making one right now that has 9. The reveal of the pleat is ideally 1/3 of the amount of fabric in the pleat (at the hip). That way, 1/3 shows, 1/3 is folded under on one side, and 1/3 on the other side. If you do it that way, the pleats meet on the wrong side of the kilt without any gap or any overlap.

So......if your hip were 42", and you did the simple thing and split it half and half pleats and apron, you'd need 21" across the back. If you had 7 pleats, each would be 3" across, and each one would require 9" of fabric (3x3). 9x7=63", or 1 3/4 yards for the pleats. The apron and underapron each take up about a yard, because of the facings and the pleat under the apron and underapron edges. So, that's perilously close to 4 yards.

Cheers,

Barb