On 2008-09-30, Steve Barker DLT wrote:

23.625

arrived at that figure by dividing 30 by 9.5 and getting about 3.15
then divided 19 by 6 and got about 3.15
then multiplied 7.5 times 3.15

Just FYI, this is a slight underestimate for the R-value.
R-value/inch goes up slightly when you compress fiberglass insulation.
This is why higher density fiberglass insulations have a higher
R-value/inch. Of course, total R-value still goes down when you
compress the insulation.

Cheers, Wayne