Insulation Calculator
Measure the area to insulate, copy the coverage figure off your package label, and get whole packages with a cutting allowance applied before the round-up. R-value guidance stays where it belongs — in prose, not fake math.
Area and package coverage
Example: a 25 × 20 ft attic with bags labeled 58 sq ft at 5% waste → 10 bags.
Package counts only — R-value selection, vapor barriers, ventilation baffles, and code-required levels are for DOE guidance, your product's instructions, and your local code office.
One honest division
The worked attic: 25 × 20 ft = 500 sq ft ÷ 58 sq ft per bag (the figure from the label) = 8.62 bags. A 5% allowance for cutting around framing, boxes, and vents lifts it to 9.05, purchased as 10 bags with 55 sq ft of coverage to spare. Change the coverage number and everything shifts — which is exactly why it is an input, not a constant.
R-value, in one paragraph and no tables
R-value measures resistance to heat flow — higher is better insulation, and stacked layers add their values together. How much your home should have depends on where it is: the US Department of Energy publishes recommended levels by climate zone (attics warrant far more than walls, cold climates more than mild ones), and local energy codes set minimums. This page deliberately reproduces none of those numbers: recommendations change with code cycles and climate mapping, so get the target from DOE's Energy Saver guidance or your code office, pick a product that delivers it, and let this tool do the one thing it is built for — counting the bags.
While the walls are open
Insulating usually means the cavities are exposed — the moment to count the drywall that closes them back up, and after that the paint. For the framing itself, the board foot calculator handles the lumber math.
Frequently asked questions
Where do I find the coverage per package?
On the label — every batt and roll package sold in the US prints its coverage in square feet, and it is the only trustworthy figure because coverage changes with the product: a higher R-value means thicker material and fewer square feet per bag, and 15 in and 23 in widths (for 16 in and 24 in framing) pack differently. That is why this tool has no built-in coverage number.
What does R-value actually mean?
Resistance to heat flow: the higher the R-value, the better the material slows heat moving through it, and values add when layers stack. It is a property to choose before you shop — the US Department of Energy publishes recommended levels by climate zone — and once chosen it determines which product you buy. This tool then counts packages of that product; it performs no thermal calculations itself.
How do I know what R-value my home needs?
It depends on your climate zone, the assembly (attic floors want far more than walls), and what is already there. DOE Energy Saver guidance and your local code office are the right sources — a quantity calculator inventing a recommendation for your house would be guessing, so this one deliberately does not.
Should I subtract the joists from the area?
No — measure the gross area. Batts are sized for the cavities between framing at standard spacing, and label coverage already reflects real installed area. The waste allowance covers the cutting around boxes, vents, and odd bays.
Does the tool cover blown-in insulation?
The same division works — blown-in bags state coverage per bag at each target R-value in a chart on the label. Find the row for your chosen R-value, enter that coverage, and the bag count follows. The depth-and-density details on the chart are the manufacturer’s spec, not something to improvise.
Measurements never leave your browser. The estimating pipeline is documented on the methodology page.