Ted,
I don't think you question can be totally answered with a firm, exact amount of fabric.

The of the amount of fabric used in a Kilt is not a set number. It does not always lend itself to a formula.

Now that I've said that my brain works best when it has numbers to work with. So here is what I do.

And please remember that this is totally different than the way a Traditional Kiltmaker does things.

A Traditional Kiltmaker takes a known amount of fabric. 4 yards double-width for example. They then lay out both Aprons, the Deep and Reverse Pleats, and then find out how much is left over.
They then use the Sett size (or one full repeat of the Tartan pattern) and depending on if they are pleating to the Stripe or to the Sett will figure out how many Setts there are in the remaining fabric and that will give them the size of the Pleat reveal. The Pleat Depth is what is left over.

What I do is determine the Pleat Reveal I want. That tells me how many Pleats the Kilt will have. I then know the width of the aprons so the total is the amount of fabric I will need. (Notice that a Traditional Kiltmaker starts with a given amount of fabric and adjusts Pleat reveal, where I set the reveal and let the total amount of fabric to change.)

For example, A Kilt I would make for myself would take 6.93 yards if pleated to the Stripe and 7.65 if pleated to the Sett. I would have aprons 16" wide at the waist and contain 26 Pleats with a 1" reveal. IF THE SETT SIZE IS EXACTLY 6".

Keep everything the same but change just the Sett size from 6" to 6 5/8" and the same Kilt will now take 7.38 yards pleated to the Stripe and 8.10 if pleated to the Sett.

NOTHING HAS CHANGED IN THESE TWO EXAMPLES BUT THE TARTAN SETT SIZE.

Now let's switch to a Box Pleated Kilt.

If everything is perfect and the creases of the Pleats meet on the outside as well as on the inside of the Kilt each pleat width will be 1/3 of the Sett.

To look well a Box Pleated Kilt should have pleats somewhere between 2" and 3.5" wide.
If we keep with the same 6" Sett as in the Knife Pleat example above the box pleated Kilt with the same Tartan has a 2" wide Pleat.

The Problem comes with the Double Box Pleats Each Pleat uses 3/5's more fabric per Pleat. This would result in Pleats only .6" wide. Not good.

So we would have to use two Setts per Pleat or 12". This results in a Pleat 2.4" wide.

But it also uses 3/5's as much fabric per Pleat.

Here are the numbers I would come up with for my example Kilt sizes from above.

A Single Box Pleated Kilt with a Hip of 42" ---
Tartan Sett = 6"
17" Aprons
13 - 2" Box Pleats
Total amount of fabric used 5.9 Kilt yards.

A Double Box Pleated Kilt with a Hip of 42" ---
Tartan Sett = 6"
18" Aprons
11 - 2.4" Box Pleats
for a total amount of fabric of 6.16 Fabric Yards.