Sewn through design TQ?

I'm kicking around making a top quilt. I want a 40*. It seems that some of the cottage mfrs. are doing a sewn through for this temp. rating. It seems that this would cause cold spots vs. making one with baffles, like Adam at HG uses. If making the sewn through design, how would I figure down fill? L x W divided by fill, as in it would just be a tube? Or. would I add the 1.5" per baffle to one layer to get the proper loft, thus one material side would be larger than the other? A little on the confused side. I got it on making one with baffles, but sewn through is confusing me a little. :confused:

It's calculated in a similar fashion to baffles. If 1.5" is your desired loft, plug that into your formula. (LxWxH)/fill power.

P.S- A sewn through design will have cold spots, which is why 40 deg is about the lowest you will see sewn through baffles. It has worked for me fine at 40 deg, but I usually wear a fleece to bed anyway.

Ryan