I'd say you need at least the amount that one more cut of the front piece of the skirt. Sandra Betzina had an old wrap skirt pattern,Vogue 7264, her technique was essentially an underlayer of the whole skirt front. The wrap was an overlay so you never had to worry about coverage (or lack thereof).
The fabric, was there a coordinating non-decorated denim avail? I'm asking cause you may be able to save $ by using that for the underlayer.

Her sizing was great for plus sizes too. I can't find it for sale, must be out of print. May have it in my stash, I can check if you like the pattern. It's reviewed at patternreview.com, just punch the pattern number in their search box.

Didn't you read my post about them? it tells how to measure and you wont need to look for a pattern either

Here is a link that might be useful: Wrap Pants 2 1/2 yards and 2 hours - -

Minnie she asked about a wrap skirt, not the wrap pants. I guess they would be made differently, not sure.

Sue

Blitsy -

Look on Ebay. Just put in a search for wrap skirt pattern. They have lots that include size 18!

Dawn