Calculating fill power from lofted down

For all the goose down gurus out there...

I have some down of unknown fill power and need to calculate how much to use in an UQ. I made a cardboard box exactly 12" x 12" x 12" and filled it with 1 oz of the down in order to calculate the cubic inches of loft it had. To make sure all of it had a chance to loft, I shook the box a bit and let it set for several minutes. It measured 7" deep or about 1000 cu in. I've never heard of 1000 fill power down, so I thought it might settle overnight. It didn't.

Have I gone about this process in a reasonable enough fashion that I can calculate my quilt based on the 1000cu in per ounce that my down lofted to? I've never calculated fill power from lofted down before.

Thanks for the help.