3/4 length UQ w/850fp down ?

This is my first time making an underquilt and I was curious of the approximate weight of 850fp down needed for a 3/4 length UQ rated to 20 degrees Fahrenheit? Any suggestions or ideas are much appreciated.

Take the length, width, and height of your UQ and plug them into the following formula:

(L*W*H)/850

This will give you a rough estimate of how many ounces of down you will need.

Most people tend to add an extra 20% of down to their quilt to prevent down drifting and give a slight temp boost as well.

For a 20°F quilt your looking at around a 2 inch chamber height.

My advice is figure how tall you want your baffles to be, then cut them a half inch shorter and add an additional 10%-20% down over what your initial height would have been.

But I'm a belt and suspenders kind of guy, I'm working on fixing that though. :D

Ultimately it depends on the dimensions of the quilt, but hammockgear lists 8oz of fill for the 20 degree phoenix underquilt

http://www.hammockgear.com/under-quilts/

Thanks for the info Cataverie!

Thanks Brucky. I did look at that sight before I posted, but I was looking for something a little more plug and play. I think they slightly overfill.