Pleat size and number

[BertMcG]

So I'm having a little trouble with the math here. If you have 13 oz tartan with a 9" sett, why are you only getting 15 pleats if you are doing one pleat per sett

Thanks Barb, I do only have 7 yards of fabric and for some reason I thought I would only have about 150" for the pleats, where it got that I don't know. After laying everything out I will have 20 pleats to the stripe using the full sett.