When trying to determine your current R-Value in the attic, use a ruler to measure the depth of the insulation and multiply the depth by the R-Value of the material.
For example, and attic with 6 inches of Modern insulation would have an estimated R-Value of 22.5 (6 inches x 3.75 R-Value per inch)
Unless you still have the packaging for the insulation used in the attic, it will be hard to measure the exact R-Value of the installed product. To calculate the R-Value use the following guidelines for estimation purposes only:
R-Value / Inch
Remember, cellulose insulation can be blown on top of existing insulation to improve R-Values without removing the already installed insulation.