Coverage chart required on the bag by 16 CFR 460.12(b)(2)
Every blown-in calculator on the internet has a coverage rate baked into it and none of them say where it came from. They do not need one. The Federal Trade Commission's R-value Rule requires the manufacturer to print the coverage chart on the bag, at six named R-values, with five specific figures on it. This page asks for those figures rather than inventing them, and then runs the two multiplications that prove the chart is internally right.
Bags, weight and depth, from your bag's own chart
ft
ft
sq ft
R
sq ft
bags
lb
lb
in
in
in
Every figure asked for here is on the package by law. If your bag does not carry a coverage chart giving these numbers, it does not comply with 16 CFR 460.12 and you should be suspicious of it.
Specification summary
Generated from on .
Reopen that address to reproduce these figures exactly.
Entered
Result
Blown depth, settled depth, and the joists under both
Worked example
A 40 by 25 ft attic to R-30, using the R-30 row of a real published coverage chart: 22.9 sq ft per bag, 43.6 bags per 1,000, 1.014 lb per sq ft, from a 23.25 lb bag, 9 in installed settling to 8.1 in.
Area. 40 × 25 = 1,000 sq ft.
Bags. 1,000 ÷ 22.9 = 44 bags.
Check one. 22.9 × 43.6 = 998, which must be 1,000. It closes.
Check two. 22.9 × 1.014 = 23.22 lb, the bag's net weight. It closes.
Weight. 1,014 lb of material lands on that ceiling.
Depth. Blow to 9 in, settling to 8.1, which is 11.1% overblow.
Two things worth carrying away. Half a ton of insulation goes on a 1,000 square foot ceiling at R-30, and it is worth knowing that before you decide the ceiling can take it. And the settled 8.1 in finishes 1.2 in below the top of a 9 1/4 in joist, so every joist in that attic is a bare thermal bridge across the whole ceiling. The R-value calculator on this site works out what that costs.
The formula
One division for the answer, and two multiplications that check the chart before you trust it:
bags = A / c c × b = 1,000 c × w = bag net weight
A
area to cover, in square feet
c
maximum net coverage per bag at your R-value, from the bag
b
bags per 1,000 sq ft, from the same row
w
minimum weight per square foot, from the same row
all four
required on the package by 16 CFR 460.12(b)(2)
The two checks are not a refinement, they are definitions. Coverage per bag times bags per thousand has to be a thousand, and coverage per bag times weight per square foot has to be what is in the bag. A chart that fails either has a typo, and a calculator that never runs them will carry the typo straight into your order.
Why this page will not give you a coverage rate
Loose fill is the one material on this site where the figure everybody guesses at is guaranteed to exist and guaranteed to be in the room with you.
16 CFR 460.12(b)(2) requires every package of loose-fill insulation sold in the United States to carry a chart giving the minimum settled thickness, the initial installed thickness, the maximum net coverage area, the number of bags per 1,000 square feet and the minimum weight per square foot, at R-13, 19, 22, 30, 38 and 49.
That figure is a property of a specific product. A dense cellulose and a loose fibreglass do not share it, and neither do two cellulose products from different mills. Any coverage rate printed on a web page is somebody else's bag applied to yours.
So this page asks for yours. It is the same discipline used here for aggregate density, truck tare weight and supplier pricing, with one difference in your favour: federal trade regulation guarantees the number is printed on the thing you are about to buy.
One published coverage chart, 2005, with its own arithmetic checked
R-value
Install to
Settles to
Max per bag
Bags per 1,000
lb per sq ft
Coverage × bags
Coverage × weight
R-50
15 in
13.5 in
13.8 sq ft
72.7
1.689 lb
1,003
23.31 lb
R-42
12.6 in
11.4 in
16.4 sq ft
61
1.419 lb
1,000
23.27 lb
R-40
12 in
10.8 in
17.2 sq ft
58.1
1.351 lb
999
23.24 lb
R-38
11.4 in
10.3 in
18.1 sq ft
55.2
1.284 lb
999
23.24 lb
R-32
9.6 in
8.6 in
21.5 sq ft
46.5
1.081 lb
1,000
23.24 lb
R-30
9 in
8.1 in
22.9 sq ft
43.6
1.014 lb
998
23.22 lb
R-25
7.5 in
6.8 in
27.5 sq ft
36.3
0.845 lb
998
23.24 lb
R-24
7.2 in
6.5 in
28.7 sq ft
34.9
0.811 lb
1,002
23.28 lb
R-22
6.6 in
5.9 in
31.3 sq ft
32
0.743 lb
1,002
23.26 lb
R-19
5.7 in
5.1 in
36.2 sq ft
27.6
0.642 lb
999
23.24 lb
R-13
3.9 in
3.5 in
52.9 sq ft
18.9
0.439 lb
1,000
23.22 lb
R-11
3.3 in
3 in
62.6 sq ft
16
0.372 lb
1,002
23.29 lb
Read 2026-09-10. First six columns quoted from the manufacturer's published chart. The last two are this page multiplying them, and both must close.
The coverage rate is on the bag, and federal law puts it there
Every blown-in calculator on the internet has a coverage rate baked into it and none of them say where it came from. They do not need one. The Federal Trade Commission's R-value Rule requires the manufacturer to print it on the package:
For all loose-fill insulation: the 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. You must also give this information for any additional R-values you list on the chart. Labels for these products must state the minimum net weight of the insulation in the package. You must also provide information about the blowing machine and machine settings used to derive the initial installed thickness information.
Five figures, at six named R-values, on every bag of loose fill sold in the United States. Minimum settled thickness, initial installed thickness, maximum net coverage area, bags per 1,000 square feet, and minimum weight per square foot. Plus the bag's net weight and the blowing machine settings the installed thickness was derived from.
So the number this calculator needs is not a number anybody has to estimate. It is a legally required disclosure sitting in your hands, it is specific to the product you bought, and a dense cellulose and a loose fibreglass will not share it.
Which is why this page asks for it rather than supplying one. The regulation also sets the tolerance, and it runs one way only:
If you are a manufacturer of home insulation, no individual specimen of the insulation you sell can have an R-value more than 10% below the R-value shown in a label, fact sheet, ad, or other promotional material for that insulation.
Ten per cent below is legal. There is no matching limit above, so a bag labelled R-30 may test at R-27 and comply. Worth knowing before you install to the minimum and no further.
A coverage chart checks itself, in two multiplications
The five figures the rule requires are not independent. Two of them are definitions, so any real chart has to close:
max sq ft per bag × bags per 1,000 sq ft = 1,000 max sq ft per bag × min lb per sq ft = the bag’s net weight
Here is a real chart with both multiplications run on every row. It is US GreenFiber Cocoon loose-fill cellulose, INS550LD, 23.25 lb bag, published 2005, and it is here to demonstrate the arithmetic rather than to tell you what your bag says:
One published coverage chart, and its own two checks
R-value
Install to
Settles to
Max per bag
Bags per 1,000
lb per sq ft
Coverage × bags
Coverage × weight
R-50
15 in
13.5 in
13.8 sq ft
72.7
1.689 lb
1,003
23.31 lb
R-42
12.6 in
11.4 in
16.4 sq ft
61
1.419 lb
1,000
23.27 lb
R-40
12 in
10.8 in
17.2 sq ft
58.1
1.351 lb
999
23.24 lb
R-38
11.4 in
10.3 in
18.1 sq ft
55.2
1.284 lb
999
23.24 lb
R-32
9.6 in
8.6 in
21.5 sq ft
46.5
1.081 lb
1,000
23.24 lb
R-30
9 in
8.1 in
22.9 sq ft
43.6
1.014 lb
998
23.22 lb
R-25
7.5 in
6.8 in
27.5 sq ft
36.3
0.845 lb
998
23.24 lb
R-24
7.2 in
6.5 in
28.7 sq ft
34.9
0.811 lb
1,002
23.28 lb
R-22
6.6 in
5.9 in
31.3 sq ft
32
0.743 lb
1,002
23.26 lb
R-19
5.7 in
5.1 in
36.2 sq ft
27.6
0.642 lb
999
23.24 lb
R-13
3.9 in
3.5 in
52.9 sq ft
18.9
0.439 lb
1,000
23.22 lb
R-11
3.3 in
3 in
62.6 sq ft
16
0.372 lb
1,002
23.29 lb
The last two columns are the test. Every row multiplies out to 1,000 and to 23.25 lb, which is the bag's stated net weight, within rounding. A chart that misses either has a typo in it, and the calculator above runs the same two checks on whatever you type in.
Read the R-30 row across as a worked example: install to 9 in, it settles to 8.1 in, one bag covers 22.9 sq ft, you need 43.6 bags per 1,000 sq ft, and at least 1.014 lb of material sits on every square foot when you are done.
What is already up there, and why it is not simply subtracted
Most blown-in jobs are top-ups over insulation that is already there, and the arithmetic people reach for is to subtract the existing R-value from the target. That is right in principle and wrong in two ways in practice.
Old insulation is not at its labelled R-value. It has settled, it has been walked on, it may have been wet, and the depth you measure is the honest input rather than whatever it said on the bag in 1994. Measure the depth in several places, low, and take the smallest.
And what is under the new layer changes what the new layer does. Blowing loose fill over old batts is normal and works. Blowing it over a vapour retarder facing upward traps moisture in the assembly, and the fix is to remove or slash the facing, not to add depth.
Do not compress what is there. Loose fill blown over compressed batts does not restore the batts, and R-value lost to compression stays lost. If the existing layer is squashed under stored boxes, the boxes are the problem.
The clean way to use this page for a top-up is to work out the R-value you are short by, then run the calculator for that difference as though the ceiling were bare.
The things that beat depth, and the one this page can see
An attic that is short on insulation is usually not the biggest problem in the attic.
Air leaks come first. Every penetration through the ceiling plane, top plates, wire holes, plumbing stacks, recessed lights and the attic hatch, moves heat by a mechanism no R-value describes. Blowing insulation over an unsealed ceiling buries the leaks where nobody can find them, which is why sealing before blowing is the standard sequence rather than a refinement.
Ventilation baffles come second. Loose fill blown into the eaves blocks the soffit vents, and a blocked soffit vent turns a vented attic into an unvented one with no design behind it. Baffles go in before the hose does.
Then depth. Which is what this page counts, and it counts it in bags rather than inches because bags are the figure that cannot settle out of the answer.
The one thing this page can see beyond depth is the joists: enter their depth and it will tell you whether the finished layer covers them. A layer that finishes below the joist tops leaves a bare wooden bridge every 16 or 24 inches across the entire ceiling.
And the whole chart is generated from two figures
Twelve rows, six columns, and almost none of it is data. Divide the settled thickness into the R-value on every row:
The same number, R-11 to R-50. About 3.7 per inch, and the small wobble is the chart rounding its thicknesses to a tenth. Now divide the settled thickness into the installed thickness:
The same number again, 1.110 on average and 1.100 to 1.119 across the twelve rows, which is a settling allowance of about 11% applied to all of them. The spread is the chart rounding thicknesses to a tenth of an inch, not a different figure per row.
So a twelve-row coverage chart carries two facts: an R per inch and a settling allowance. Everything else on it is those two run through the definitions.
That is worth knowing for a practical reason. When you compare two products' charts you are comparing two numbers, not twelve, and the one that matters is the R per inch, because it decides the depth and the depth decides whether it fits above your joists.
Install thickness against settled thickness, and which one you check
The rule requires both, and they are different jobs. The initial installed thickness is how deep it goes in on the day. The minimum settled thickness is what is left after it has compacted under its own weight, and it is the depth the R-value belongs to.
On the chart above that is 9 in going in for 8.1 in settled at R-30: you blow it 11.1% deeper than the number you are aiming at.
So a depth check on installation day passes at the installed figure and a depth check next year passes at the settled one, and an inspector measuring the wrong one against the wrong day gets the wrong answer in either direction.
The reliable check is not depth at all, it is bag count. Count the empty bags. The rule requires bags per 1,000 square feet on the label precisely because it is the figure that cannot settle, cannot be eyeballed and cannot be argued with, and it is why blown insulation jobs are specified that way.
The manufacturer's own note on the example chart says the same thing from the other side:
Coverage chart is based on settled thickness and is for estimating purposes only. Do not exceed maximum square foot coverage per bag. Actual coverage will be influenced by job conditions and application techniques and may vary as much as 10% without significantly affecting the stated R-Value. Failure of the installer to provide at least the required number of bags 1,000 square foot and at least the minimum thickness may result in a lower installed R-Value.
The sources, and the one this page will not supply
Read 2026-09-10.
16 CFR Part 460, Labeling and Advertising of Home Insulation (the R-value Rule), Federal Trade Commission. Sections 460.8, 460.11, 460.12 and 460.13. Requires every loose-fill insulation package to carry a coverage chart giving minimum settled thickness, initial installed thickness, maximum net coverage, bags per 1,000 square feet and minimum weight per square foot, at six named R-values. Also sets the tolerance: an individual specimen may not be more than 10% below the labelled R-value.
Loose Fill Insulation Coverage Chart, Cocoon INS550LD, US GreenFiber, product specification sheet dated 2005, hosted by the National Association for State Community Services Programs. One real coverage chart in the form 16 CFR 460.12(b)(2) requires, used here to show that the arithmetic on such a chart closes and what the two figures behind it are. It is twenty-one years old and is NOT presented as current product data. Read your own bag.
This page publishes no coverage rate of its own. It cannot: the figure is a property of a specific product, the regulation requires that product to disclose it, and any number printed here would be somebody else's bag applied to yours.
The same reasoning runs through this site for aggregate density, truck tare weight and supplier pricing. The difference here is that for once the figure is guaranteed to exist and guaranteed to be in the room with you, because federal trade regulation puts it there.
Coverage is not compliance. What R-value you need is a code question, and it is on the R-value calculator, where the answer depends on your climate zone and on which edition of the energy code your jurisdiction enforces.
Frequently asked questions
How many bags of blown insulation do I need?
Divide the area by the maximum net coverage per bag at your target R-value, and round up. Both figures are on the bag: 16 CFR 460.12(b)(2) requires the coverage chart to give maximum net coverage and bags per 1,000 square feet at R-13, 19, 22, 30, 38 and 49. Do not use a coverage rate from a web page, including this one, because the number is specific to the product you bought.
Where do I find the coverage chart?
Printed on the package. The Federal Trade Commission's R-value Rule requires it on every bag of loose-fill insulation sold in the United States, along with the bag's minimum net weight and the blowing machine settings the installed thickness was derived from. If your bag has no such chart, it does not comply with the rule.
How deep does blown insulation need to be?
Deeper going in than it will be afterwards. The chart gives an initial installed thickness and a minimum settled thickness, and the R-value belongs to the settled one. On the published chart used as an example here the difference is about 11%, so 9 inches goes in to leave 8.1. Check the job by counting empty bags rather than by measuring depth, because depth changes and a bag count does not.
How much does blown insulation weigh?
The chart tells you, per square foot, at each R-value, because the rule requires it. On the example chart R-30 is 1.014 lb per square foot, so a 1,000 square foot attic takes just over half a ton of material. Worth knowing before you decide the ceiling framing can take it.
Is fibreglass or cellulose better for blowing?
This page does not answer that, and any page that does without naming a product is comparing categories rather than materials. What it does do is let you put two products' actual charts side by side, which is the comparison that means something: the R per inch decides the depth, and the depth decides whether it fits above your joists.
Can I blow new insulation over old?
Usually yes, and it is the normal way to top up an attic. Two cautions. Measure the existing depth rather than trusting an old label, because settled and compressed insulation is not at its labelled value. And if the old layer has a vapour retarder facing upward, that facing needs removing or slashing before you bury it.
Does the R-value on the bag have a tolerance?
Yes, and it runs one way. 16 CFR 460.8 says no individual specimen may be more than 10% below the R-value shown on the label. There is no matching limit above, so a product labelled R-30 may legally test at R-27. Installing to the minimum and no further puts you at the bottom of that tolerance.
Why do two calculators give me different bag counts?
Because they are using different assumed coverage rates, and neither says so. The coverage rate is not a property of blown insulation, it is a property of one product from one manufacturer, and the difference across products at the same R-value is large. Use your own bag's chart and the disagreement disappears.
Check these numbers yourself
16 CFR Part 460, Labeling and Advertising of Home Insulation (the R-value Rule)Federal Trade Commission, sections 460.8, 460.11, 460.12 and 460.13, read 2026-09-10. Requires every loose-fill package to carry a coverage chart giving minimum settled thickness, initial installed thickness, maximum net coverage, bags per 1,000 square feet and minimum weight per square foot at R-13, 19, 22, 30, 38 and 49, plus the bag's net weight and the blowing machine settings used. Section 460.8 sets the tolerance: an individual specimen may not be more than 10% below the labelled R-value, with no matching limit above.
Loose Fill Insulation Coverage Chart, Cocoon INS550LDUS GreenFiber product specification sheet dated 2005, hosted by the National Association for State Community Services Programs, read 2026-09-10. One real coverage chart in the form the rule requires, used here to demonstrate that the arithmetic on such a chart closes and to show what the two underlying figures are. It is twenty-one years old and is NOT presented as current product data.
How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.
Figures on this page last checked against the source documents on 2026-09-10. Codes are amended locally; confirm against the edition your jurisdiction enforces.
This page publishes no coverage rate of its own and will not. The figure is a property of a specific product and 16 CFR 460.12(b)(2) requires that product to disclose it on the package. The example chart shown is dated 2005, is a single manufacturer's product, and is present to demonstrate the arithmetic rather than to tell you what your bag says. What R-value you need is a separate, code question answered on the R-value calculator, and it depends on your climate zone and on which edition of the energy code your jurisdiction enforces.