What R-value should I target for my attic?

That's set by the International Energy Conservation Code as amended by your state or local jurisdiction, and varies by climate zone and whether the work is new construction or a retrofit. Check your local building department or the DOE's climate zone map for the number that applies to your project — this calculator doesn't recommend one.

Why doesn't this calculator just tell me the coverage per bag?

Because federal law already puts that number directly in your hands. 16 CFR 460.12 requires every bag of loose-fill insulation to carry a label with a coverage chart — bags per 1,000 square feet at R-values of 13, 19, 22, 30, 38, and 49. That's the actual, correct-for-your-product number; anything this calculator asserted instead would be a guess competing with a legally required fact already printed on your bag.

Can I calculate my R-value by multiplying R-per-inch by my installed depth?

No — 16 CFR 460.17, the FTC's rule on what installers must disclose to customers, states plainly not to do this. Settling and compression mean loose-fill insulation doesn't perform at a constant rate per inch all the way through a deep pile. Use the settled-thickness and coverage figures on your bag's label chart instead.

What's the difference between installed thickness and settled thickness?

Installed thickness is how deep the material sits right after blowing. Settled thickness is the lower depth it's expected to hold at after it compresses under its own weight over the following weeks — the label's coverage chart is built around that settled figure, not the fluffier depth on day one.

How much insulation do I need to top up an existing attic?

This calculator doesn't compute that directly — estimating a top-up amount by subtracting your current R-value from your target and converting the difference to a depth is the same R-per-inch calculation 460.17 warns against. Check your bag's own instructions for adding insulation over an existing layer, or get an on-site measurement from an installer who can assess your actual current depth and R-value.

Do I need baffles for blown-in attic insulation?

Yes, at every soffit vent, installed before you blow insulation in. Without them, blown material buries the vents and blocks the airflow they're there to provide, which is a real contributor to attic moisture and ice-damming problems. Recessed lights and chimneys need their own clearance too — check the fixture's rating and your local code.

Why doesn't this calculator add a waste percentage?

There's no cited source for a typical loose-fill waste margin beyond what your bag's own coverage chart already accounts for, so this calculator defaults to 0% rather than assert an unsourced number. Add your own margin in the waste field if you want a buffer before running out mid-job.

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Blown-In Insulation Calculator

Every bag of loose-fill insulation sold in the US is legally required to carry a coverage chart — bags per 1,000 square feet at R-values of 13, 19, 22, 30, 38, and 49, printed right on the package under 16 CFR 460.12, a Federal Trade Commission regulation. That's the number this calculator uses, not a figure of its own: this page asserts nothing about coverage, target R-value, or how much insulation you need — it just divides your attic's area by whatever coverage number your actual bag states for your actual target R-value. Enter your attic's square footage and that coverage figure, and get a bag count. See the guidance below for the one calculation the FTC specifically warns against, why settled and installed thickness are different numbers, and what to check before you blow insulation in.

Your room

LengthWidthUnit

Waste (%)This calculator doesn't assume a waste margin — there's no cited source for how much loose-fill insulation is typically lost to settling variance or an uneven attic floor beyond what the label's own coverage chart already accounts for. Leave this at 0% to match the math exactly, or add your own margin if you want a buffer before you run out mid-job.

Bag coverage at your target R-value (sq ft)Read this directly from your bag's label chart — 16 CFR 460.12 requires it to be printed on every bag. There's no standard figure to default to; use the number for your specific bag and target R-value.

Enter your room's dimensions above to see results.

How it's calculated

The calculator adds your waste percentage (0% by default — see below for why) to your attic's area, then divides that by your bag's coverage at your target R-value, rounding up to a whole bag, since a partial bag still has to be bought. That's the entire calculation. Nothing here estimates coverage, computes an R-value, or converts a thickness into a coverage figure — the coverage number is the one thing this calculator asks you to bring with you, read directly off your bag's federally required label chart, because no calculator can know which product, which manufacturer, or which R-value tier you're buying at.

Worked example

A 1,200 sq ft attic, with a bag whose label states 40 sq ft of coverage per bag at your target R-value: at the 0% waste default, adjusted area stays 1,200 sq ft. Bags needed = 1,200 ÷ 40 = 30 bags exactly. Change the coverage number to whatever your actual bag states — a different product, or a different target R-value on the same bag's own chart, gives a different coverage figure and a different bag count from the same 1,200 sq ft attic.

The label has the number — read it, don't calculate it

Every bag of loose-fill insulation sold in the US carries a coverage chart by federal law. 16 CFR 460.12, a Federal Trade Commission trade regulation rule, requires the label to show minimum settled thickness, initial installed thickness, maximum net coverage area, number of bags per 1,000 square feet, and minimum weight per square foot — at R-values of 13, 19, 22, 30, 38, and 49. That chart is the number to use for this calculator's bag-coverage field, not a figure from this page or any other calculator. Read the row for your target R-value off your actual bag, and enter that coverage number above.

There's one specific mistake the FTC's own installer-disclosure rule names directly: 16 CFR 460.17 states plainly that you should not multiply the R-value for one inch of insulation by the number of inches you installed to estimate your R-value. An inch of loose-fill material doesn't perform at a constant R-per-inch rate all the way through a deep pile — settling, density, and how the material compresses under its own weight all change that relationship, which is exactly why the label's coverage chart is built from tested settled performance at each R-value tier, not a linear formula. If you've ever heard a rule of thumb like "this insulation is R-3.5 per inch, so 12 inches gets you R-42," that's the calculation the FTC is specifically telling installers not to make.

The label lists two different thickness numbers, and they matter for different reasons. Initial installed thickness is how deep the material sits immediately after blowing, before it settles under its own weight and air movement over the following weeks. Minimum settled thickness is the depth it's expected to hold at once it does — lower than the installed depth, because loose-fill genuinely compresses over time. The coverage chart's bags-per-1,000-square-feet figures are built around reaching that settled thickness at each R-value, not the fluffier depth right after installation, so don't judge a fresh install by how deep it looks on day one; the number that matters is what it settles to.

If you're topping up existing insulation rather than starting from a bare attic floor, this calculator doesn't compute that for you — figuring out how many bags close the gap between your current and target R-value by estimating a depth and multiplying by an R-per-inch figure is exactly the calculation 460.17 warns against, so building that math into this page would mean making the same mistake the regulation exists to prevent. Instead, check your bag's own label and installation instructions for guidance on adding insulation over an existing layer, or get a target coverage figure from an installer who can measure your actual existing depth and R-value on site.

Two things to check before you blow insulation in, neither of which this calculator estimates. Soffit vents need baffles (sometimes called rafter vents) installed before insulation goes in, or the blown material will bury the vents and block the airflow they're there to provide — that airflow is part of how an attic avoids moisture buildup and ice damming, so it's worth getting right before the bags go in, not after. Recessed lighting fixtures and chimneys also need clearance from insulation — how much, and whether a fixture is even rated to have insulation in contact with it, depends on the specific fixture and your local code, not a number this calculator can give you. Check the fixture's own rating and your local building department for both.

Target R-value itself is a code question this page doesn't answer. It's governed by the International Energy Conservation Code as amended by your state or local jurisdiction, and it varies by climate zone and by whether the work is new construction or a retrofit — the DOE publishes climate-zone recommendations, which are a useful reference but not the same thing as your jurisdiction's actual requirement. Confirm your target R-value with your local building department or the DOE's climate zone map first, then find that R-value's row on your bag's label chart, and enter that row's coverage number above.

Common mistakes

Multiplying an R-per-inch figure by your installed depth to estimate R-value. 16 CFR 460.17 names this specific calculation as a mistake — settling and compression mean insulation doesn't perform at a constant rate per inch all the way through. Use the settled-thickness figure on your bag's label chart instead.
Reading a bag coverage number off someone else's bag, an old memory, or a different product's label. Coverage varies by manufacturer, product, and target R-value — the number that's correct for your job is on the bag you're actually buying, at the row for your actual target R-value.
Judging coverage or thickness right after blowing, before the material settles. The label's coverage chart is built around settled thickness, not the fluffier installed depth on day one — a fresh install that looks deep enough can settle to less than your target.
Guessing at a target R-value instead of checking your local energy code. Target R-value is governed by the International Energy Conservation Code as amended locally, and varies by climate zone and whether it's new construction or a retrofit — check your local building department or the DOE's climate zone map, not a preset on this page.
Blowing insulation over soffit vents without baffles installed first. Buried vents can't provide the airflow they're there for, which is a real contributor to attic moisture and ice-damming problems down the line.
Estimating a top-up quantity by subtracting current R-value from target and converting the difference to a depth. That's the same R-per-inch calculation 460.17 warns against — check your bag's own instructions for adding insulation over an existing layer, or get an on-site measurement from an installer.

Where the figures come from

This page's sources back up that these labeling and disclosure requirements exist and what they require — not a coverage number itself, since federal law deliberately puts that number on the package instead of leaving it to be estimated. 16 CFR 460.12 requires every package of loose-fill insulation to carry a chart showing minimum settled thickness, initial installed thickness, maximum net coverage area, bags per 1,000 square feet, and minimum weight per square foot, at R-values of 13, 19, 22, 30, 38, and 49; batts and blankets are labeled with R-value, dimensions, and total square feet in the package instead. 16 CFR 460.17 covers what an installer's receipt must show, and separately states that an R-per-inch figure should not be multiplied by installed depth to estimate R-value. Both are Federal Trade Commission trade regulation rules under 15 U.S.C. 41 — this site's first federal regulation cited as a source, and a different kind of citation from the density and coverage figures elsewhere on this site: those back up a measured physical fact, this backs up a legal requirement that the correct fact already be in the reader's hands.

FAQ

What R-value should I target for my attic?: That's set by the International Energy Conservation Code as amended by your state or local jurisdiction, and varies by climate zone and whether the work is new construction or a retrofit. Check your local building department or the DOE's climate zone map for the number that applies to your project — this calculator doesn't recommend one.
Why doesn't this calculator just tell me the coverage per bag?: Because federal law already puts that number directly in your hands. 16 CFR 460.12 requires every bag of loose-fill insulation to carry a label with a coverage chart — bags per 1,000 square feet at R-values of 13, 19, 22, 30, 38, and 49. That's the actual, correct-for-your-product number; anything this calculator asserted instead would be a guess competing with a legally required fact already printed on your bag.
Can I calculate my R-value by multiplying R-per-inch by my installed depth?: No — 16 CFR 460.17, the FTC's rule on what installers must disclose to customers, states plainly not to do this. Settling and compression mean loose-fill insulation doesn't perform at a constant rate per inch all the way through a deep pile. Use the settled-thickness and coverage figures on your bag's label chart instead.
What's the difference between installed thickness and settled thickness?: Installed thickness is how deep the material sits right after blowing. Settled thickness is the lower depth it's expected to hold at after it compresses under its own weight over the following weeks — the label's coverage chart is built around that settled figure, not the fluffier depth on day one.
How much insulation do I need to top up an existing attic?: This calculator doesn't compute that directly — estimating a top-up amount by subtracting your current R-value from your target and converting the difference to a depth is the same R-per-inch calculation 460.17 warns against. Check your bag's own instructions for adding insulation over an existing layer, or get an on-site measurement from an installer who can assess your actual current depth and R-value.
Do I need baffles for blown-in attic insulation?: Yes, at every soffit vent, installed before you blow insulation in. Without them, blown material buries the vents and blocks the airflow they're there to provide, which is a real contributor to attic moisture and ice-damming problems. Recessed lights and chimneys need their own clearance too — check the fixture's rating and your local code.
Why doesn't this calculator add a waste percentage?: There's no cited source for a typical loose-fill waste margin beyond what your bag's own coverage chart already accounts for, so this calculator defaults to 0% rather than assert an unsourced number. Add your own margin in the waste field if you want a buffer before running out mid-job.