Is there a reference chart somewhere that compares "inches of loft" to a corresponding "R-value"

I have a Therm-a-rest Trail Lite (size L) that fits better than reasonably well into my MEC Raven Wide -7C (20F) mummy bag.

The T-Rest has an R-value of 3.4 and I'd like to know how many inches of down loft it is equivalent to, and through that, the approximate temp. comfort expectations.

(I've just purchased my first hammock and have yet to spend a night in one, so I'm reaaaaally fresh at this ... and yes I realize that I'll prolly end up with a UQ and TQ soon enough anyway.)