wall-framing-takeoff counted wall-cavity insulation from the framing it placed, but left the attic out. insulation.attic now sizes loose fill: settled depth is the target R-value divided by the product's R per inch (R-38 at R-3.8 per inch is 10 in), volume is ceiling area times depth plus waste. The area comes from the plan's ceiling rectangles, the drywall ceilings or, last, the roof footprint.
Two figures vary by product, so the tool does not invent them. R per inch defaults to 2.5 and the output says it was assumed. Bags are counted only if you type the bag's cubic feet; otherwise you get depth and cubic feet. Tests check the arithmetic by hand; no real bag chart has been compared, and baffles and eave compression are not modelled.