how to figure out outter sheel dimensions on an underquilt?

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I am working on the plans for a new diy underquilt and am wondering how to figure out the outter shell dimensions.

My inner shell dimensions, not including seam allowance are 43.5 x 52 with 2.5 inches of loft. I am going to make my channels separate and attach before stuffing so those wouldn't come into play. I will have 5 baffles that are 7.5 in wide and running the full length of the quilt and two at 3 inches on either side.

I just want to cut wider on the outter shell and not longer. This is my first down quilt and I don't want to go crazy with over complicating it if I can help it.

So what do you say, how do I figure out the outter shell to allow for the 2.5" of loft I want without compression issues but not to loose, loosing the insulation of the down?

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Also I forgot to mention that I am using no-see-um between the baffles.

[MAD777]

Inside width (43.5") divided by pi (3.14) plus thickness (2.5") all multiplied by pi (3.14). Finally add twice the baffle height (the two outside edges of the quilt are "external" baffles). Then of course, add you seam allowances.

For your quilt, the outer width should be about 56" depending on your baffle height, plus your seam allowances.

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Thank you!

[GregB]

There is a great spreadsheet somewhere here on the forums which I'm using to design my underquilt. You enter the length, width, baffle height, loft height and number of baffles and it tells you everything you need to know including how many ounces of down go into each baffle (it even calculates for different down fills).

I'll try to track it down and post a link here.

Found it! It's in this thread

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Blast from the past here. Nice resource. Thank you!