With my Euro pleat drapery, I used 4" Buckram. I made a 4" double fold for the header and a 4" double fold for the hem. I used 4-1/4" for the pleats. I believe mine are called 2 finger pleats tacked at the top. You mention wanting 3 finger pleats, so you may need a little more in order to get that 3rd pleat. I used 4" for the spaces.

Here are the terms I noted that (I think) describe the type of pleat I used (different terms describing the same thing):

Double Pinch Pleat

Parisian Pleat

Euro Pleat

2 Finger Pleat Tacked at Top

I am having difficulty attaching photos today : (

Here is the other pic that did not go through in my last post.

Thanks a lot, that's very helpful. I will use a ~ 4" buckram. I made a mistake in my initial post re the size of the pleats v. the size of the spaces (converting inches to cm and then back to inches...), the proportion indicated in the calculator is in fact as expected.