Attic insulation levels are measured by R-Value, which indicates resistance to heat flow. Most attics should be insulated to R-38, or about 10 to 14 inches, depending on the insulation type.
To cut fiberglass insulation, use a sharp utility knife and a straightedge to ensure a clean, straight cut.
Insulation should face the living space, with the vapor barrier (the paper or foil backing) towards the interior to help control moisture.