For differential cut you use the formula:
- b1 = Inner Baffle spacing
- b2 = Outer Baffle spacing
- H = Baffle height
- L = Lenght of Baffle
- FP = Fill Power of Down used
Your finding the area of Trapezoid and then finding the volume of a trapezoidal solid. This will give you amount of down per each chamber.
I can tell you that I made my UQ with exactly the same measurements as the OP.
- Inner Baffle Spacing 5.5 inches
- Outer Baffle Spacing 6.25 inches
- Baffle height 2 inches
- 8 Chambers
- 1.25 ounces of 850FP down per chamber
Honestly though a little more, maybe 1.5oz per chamber, wouldn't hurt to fill it out a bit more.