If you scroll to the bottom of the link I'm providing, under 'Support Tools' click on 'Yardage Estimator'.

A PDF will open and on page 3 are the yardage estimates for drapery panels.

hth!

Here is a link that might be useful: Yardage Estimator

Are you calculating square yards or linear yards?

Are you going to allow for any "stack" so that the drapes clear the window when they are open? Are you using a pattern with a repeat? How much fullness do you want? How high will you want to hang them? All these questions (and probably more) need to be answered before you buy your fabric. And by the way, sometimes you can buy drapes from places like Ikea and Target for much less than you can make them.

Roughly guessing, you are going to want to double the width of the window for the drape, though you could go more. So 41" would mean you need at least 82" finished. Most decorator fabric is 54" wide so with seam allowance and finishing the sides you will need will need 2 lengths of fabric for each window. Guessing 8" for the hem (4" hem doubled is standard) and depending on what you want to do with the top, let's say 4" would give you a header and a rod pocket. So 84" + 8" + 4" means each drop needs to be 96" long or 2 3/4 yards...so figure 5 1/2 to 6 yards for each window. The 6 yards will give you a little extra if you wanted to make tie backs.

But you really need to decide on what you want to do with the drape at the top to be sure.

I agree that buying panels is very cost effective. I have been looking at jcpenney since they went to the new pricing scheme and the prices on their stuff is really excellent.

With a standard 84 inch length drape, you almost can't make them cheaper than you can buy them.

You probably can buy them cheaper, but if you want something specific or different, or to use really pretty fabric, you may need to make or have them made. The only problem with making them youself, is that you can't return them if you decide they aren't quite right. You can change things if you want to though.

Don't feel bad you have trouble with calculations. I sew a fair amount and always by the seat of my pants!
Do you have Tuesday Morning and Marshall's near you? I was patient in replacing my custom drapes (they had become too formal for me) and found great luck with those stores!

Are you planning on closing the drapes daily for privacy/light control or do you want stationary panels? I don't like a lot of bulk in my stationary panels so I use less fabric than the usual calculations call for.

I recently made unlined panels for 2 windows and I could have purchased them for less than what it cost me to make them but I just couldn't find the right color in a lightweight cotton.

As Annie mentioned, JCP has excellent pricing (ask about sales) and I was surprised to find they've added a huge selection in colors and styles. Last week I purchased Cindy Crawford's Sonoma panels and am more than pleased with them! They hang nicely, are lined, and I didn't have to spend hours sewing and trying to get them perfectly square!

From jcp website, grommeted 84" panels are $18 each or $36 per window. Unless you can buy fabric for $6 per yard or less, (ignoring the time and effort to sew, thread, etc.) you would be better off with the ready made.

As music teacher suggested, make them only if you want something special and specific.

I've made all of my own window treatments, but that was because I chose specific fabrics as the jumping off point for each room. It's a fair amount of work and time...fortunately I enjoy doing it.

Here is a link that might be useful: Grommeted panels