How many bags of insulation do I need?

Divide the area, plus a little extra, by the square feet in one bag. A 60 ft run of 8 ft wall is 480 sq ft; with 5% extra that is 504 sq ft, and a typical 106.56 sq ft bag of R-13 batts gives 5 bags. The sq ft per bag changes with the product, so use the figure on the bag you are buying. Blown-in is counted by the chart for its R-value instead: bags per 1,000 sq ft × the area ÷ 1,000.

Do I subtract the studs or joists?

No. A batt’s printed coverage is its own area, which includes the strip it covers over the framing, and the calculator uses the area of the wall or attic as measured. Subtract doors, windows and hatches, since you do not insulate those. Cutting around wires, boxes and pipes is what the waste allowance is for.

Should I use 15 in or 23 in batts?

Studs 16 in on center leave a 14.5 in gap, so wall batts are made 15 in wide for a snug friction fit; studs 24 in on center take a 23 in batt. The R-30 and R-38 attic batts that are 48 in long are 16 and 24 in wide for joists at 16 and 24 in on center. Pick the spacing here and the calculator uses the typical bag for that width.

How many square feet are in a bag of batts?

It depends on the R-value, width, length and how many batts the pack holds. For Owens Corning EcoTouch PINK as listed by distributors, a bag of R-13 for 16 in studs is 106.56 sq ft, R-19 is 77.5 sq ft and R-30 is 53.33 sq ft, and the thicker the batt, the fewer sq ft in a bag. These are typical figures, not a standard: the bag in your hand is the truth. Type its number into the sq ft per bag field.

How are blown-in insulation bags counted?

From the manufacturer’s coverage chart: it lists, for each R-value, the bags per 1,000 sq ft and the minimum thickness once the insulation has settled. For AttiCat to reach R-38 the chart says 19 bags per 1,000 sq ft and 13.5 in; a 40 × 25 ft attic (1,000 sq ft) needs 19 bags, or 20 with 5% extra. R-49 is 25 bags per 1,000 sq ft and R-60 is 31.5.

Why does the thickness matter as well as the bags?

The R-value on the chart is only reached when you install the required number of bags and the insulation is at least the minimum thickness, which is why the chart lists both. Spreading the bags over more area than the chart allows gives a thinner, lower-R layer. Staple depth markers to the rafters or joists so you can check the depth as you blow.

My bag’s coverage chart does not match AttiCat. What do I do?

Use yours. Coverage charts differ by product (fiberglass or cellulose) and density. Find your target R-value on your bag’s chart, copy the bags per 1,000 sq ft into the bags per 1000 sq ft field, and the bag count follows. For example, 22 bags per 1,000 sq ft over a 40 × 25 ft attic is 24 bags with 5% extra, against 20 for the AttiCat chart.

What R-value should I aim for?

It depends on your climate zone, the part of the house and what you already have. The U.S. Department of Energy publishes a table of recommended R-values for attics, floors and walls by climate zone, which ENERGY STAR hosts as Recommended Home Insulation R-Values (linked in the sources). Check that table and your local code for your zone; this page does not copy the numbers.

How much waste should I allow?

The 5% and 10% choices are rules of thumb, not manufacturer figures. 5% suits open walls and attic floors with few cuts; 10% suits walls with many cuts around windows, wiring and boxes, or an attic with lots of obstructions. Bags only come whole, so the rounding up adds some more.

Insulation Calculator: How Many Bags of Batts or Blown-In Do I Need?

Bags = the area × 1.05 ÷ the sq ft on one bag, rounded up. For 60 ft of 2 × 4 wall 8 ft high (480 sq ft) with R-13 batts for studs 16 in on center, a typical bag of 106.56 sq ft gives 5 bags with 5% extra: type the sq ft printed on your bag to be exact. For a blown-in attic, 1,000 sq ft takes 19 bags of Owens Corning AttiCat to reach R-38, laid at least 13.5 in deep once settled: a 40 × 25 ft attic is 20 bags with 5% extra. Coverage charts differ by product, so enter your bag’s own numbers if they differ.

Figures based on the sources listed belowUpdated 2026-10-04How we calculate

Length (or total wall length)

Width (or wall height)

Waste

Simple, few cuts (5%)Many cuts, obstructions or uneven attic (10%)Custom

Type of insulationBatts: enter the total wall length and the wall height, or the attic length and width. Blown-in: enter the attic length and width.

Batt R-valueR-13 and R-15 are made for 2 × 4 walls, R-19 and R-21 for 2 × 6 walls, and R-30 and R-38 for attic floors. Thicknesses are Owens Corning EcoTouch PINK; other makers differ a little.

Stud or joist spacingPicks the batt width, 15 in for 16 in spacing and 23 in for 24 in (R-30 and R-38 attic batts are 16 and 24 in wide), which sets the typical bag coverage.

Coverage on your bag, or 0 for the typical figure (sq ft)

Bag sizes vary with the product, facing and pack. Type the coverage printed on your bag for an exact count; leave 0 to use a typical Owens Corning bag for the R-value and spacing.

Price per bag (optional)

Buy 5 bags

480 sq ft + 5% waste = 504 sq ft

Batt thickness for R-13 (typical): 3.5 in

How this number is calculated

480 sq ft + 5% waste = 504 sq ft ÷ 106.56 sq ft per bag = 5 bags

Shopping list

Insulation knife
Respirator or dust mask (N95)
Safety glasses
Disposable coveralls and gloves
Attic insulation depth markers
Attic baffles (rafter vents)
Fire-block expanding foam sealant
Staple gun

Show diagram

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AttiCat blown-in coverage chart by R-value

Owens Corning AttiCat, 27.5 lb bag: the bags per 1,000 sq ft, maximum net coverage per bag and minimum settled thickness as published in the manufacturer’s chart. The last column is worked by this calculator for a 40 × 25 ft (1,000 sq ft) attic with 5% extra. Other products have their own charts.
R-value	Bags per 1,000 sq ft	Sq ft per bag (max)	Minimum settled thickness	Bags for 1,000 sq ft + 5%
R-13	5.9	169.8	5 in	7
R-19	9	110.7	7 in	10
R-22	10.5	94.8	8 in	12
R-26	12.6	79.3	9.5 in	14
R-30	14.6	68.5	10.75 in	16
R-38	19	52.6	13.5 in	20
R-44	22.4	44.6	15.5 in	24
R-49	25	39.9	17 in	27
R-60	31.5	31.8	20.5 in	34

Blown-in bags by attic size and R-value

AttiCat bags with 5% extra, worked by this calculator from the chart above. The R-value is reached only with all the bags and at least the minimum thickness.
Attic floor	R-30	R-38	R-49	R-60
20 × 20 ft (400 sq ft)	7	8	11	14
30 × 25 ft (750 sq ft)	12	15	20	25
40 × 25 ft (1,000 sq ft)	16	20	27	34
50 × 30 ft (1,500 sq ft)	23	30	40	50
60 × 40 ft (2,400 sq ft)	37	48	63	80

Typical batt bags and coverage by R-value

Owens Corning EcoTouch PINK batts as listed by distributors: the typical sq ft per bag the calculator starts from, for framing 16 in and 24 in on center. Bags for a 1,000 sq ft area are worked by this calculator with 5% extra. Your bag may differ: type its sq ft.
R-value	Thickness	Batt width (16 / 24 in)	Typical sq ft per bag (16 / 24 in)	Bags for 1,000 sq ft (16 / 24 in)
R-13	3.5 in	15 in / 23 in	106.56 / 178.25	10 / 6
R-15	3.5 in	15 in / 23 in	67.8 / 104	16 / 11
R-19	6.25 in	15 in / 23 in	77.5 / 118.83	14 / 9
R-21	5.5 in	15 in / 23 in	77.5 / 89.13	14 / 12
R-30	9.5 in	16 in / 24 in	53.33 / 80	20 / 14
R-38	12 in	16 in / 24 in	42.7 / 64	25 / 17

Batt bags for common wall sizes (framing 16 in on center)

Typical bags with 5% extra, worked by this calculator for studs 16 in on center. Measure the walls (total length × height), take off the openings, and use your bag’s real coverage for an exact count.
Wall	R-13 bags	R-15 bags	R-19 bags	R-21 bags
40 ft of wall × 8 ft (320 sq ft)	4	5	5	5
60 ft of wall × 8 ft (480 sq ft)	5	8	7	7
100 ft of wall × 8 ft (800 sq ft)	8	13	11	11
150 ft of wall × 9 ft (1,350 sq ft)	14	21	19	19

Methodology & assumptions

The area is the length × the width you enter (the total length of the wall × its height, or an attic's length × width) less any openings, then increased by the waste allowance (5% or 10%, estimates for trimming around obstructions) and divided by the coverage of one bag, rounded up. Batts: the coverage is the square feet printed on the bag. The default is a typical Owens Corning EcoTouch PINK Fiberglas bag for the R-value and the spacing, taken from distributor listings of that product: R-13 106.56 sq ft at 16 in and 178.25 at 24 in; R-15 67.8 sq ft at 16 in and 104 at 24 in; R-19 77.5 sq ft at 16 in and 118.83 at 24 in; R-21 77.5 sq ft at 16 in and 89.13 at 24 in; R-30 53.33 sq ft at 16 in and 80 at 24 in; R-38 42.7 sq ft at 16 in and 64 at 24 in. Bag sizes vary by pack, facing (kraft, foil or unfaced) and maker, so type your own bag’s figure whenever you have it; that figure always wins. A batt is 1 in narrower than the framing spacing so it holds by friction (15 in for studs 16 in on center, 23 in for 24 in; the longer R-30 and R-38 attic batts are 16 and 24 in wide), and the sq ft on the bag is the batt’s own area, so the framing is not subtracted from the area. Blown-in: bags = the area × bags per 1,000 sq ft ÷ 1,000 for the target R-value, with the bags per 1,000 sq ft and the minimum settled thickness taken from the Owens Corning AttiCat coverage chart for its 27.5 lb bag (see the table). The chart is for an attic floor that is open and level and for loose fill blown at its labeled density: the stated R-value is reached only when both the number of bags and at least the minimum thickness are installed, so do not stretch the bags to cover more area. Other products, such as cellulose, have different charts: copy the bags per 1,000 sq ft for your R-value from your bag into the override. The calculator counts a full new layer to the target R-value; if you are topping up existing insulation, work out the R-value to add (the target less what you have) and be aware that the result is an estimate. The bags and thicknesses are material counts, not a design: climate zone, code and moisture or ventilation details set what your house needs. The metric toggle shows lengths in m and areas in m².

Owens Corning, AttiCat Expanding Blown-in Insulation coverage chart (bags per 1,000 sq ft, maximum net coverage per bag and minimum settled thickness for R-13 to R-60, 27.5 lb bag)
Owens Corning, AttiCat Expanding Blown-in Insulation Product Data Sheet and coverage chart (copy hosted by a distributor)
Owens Corning, EcoTouch PINK Fiberglas Insulation product data sheet: R-11 to R-49, thicknesses of 3.5 to 14 in, batts and rolls in 15, 16, 23 and 24 in widths
Distributor listings of Owens Corning EcoTouch PINK batt bags (for example Dealer’s Choice Distribution): the typical sq ft per bag used as the default. These vary by pack and facing, so treat them as typical figures and check your bag
ENERGY STAR, Recommended Home Insulation R-Values: the U.S. Department of Energy climate-zone table of R-values for attics, floors and walls; this page links to it and does not copy its numbers

How to calculate insulation bags

Measure the area. For walls, add up the length of the walls and multiply by the height. For an attic floor, multiply its length and width. Subtract doors, windows and hatches.
Pick batts or blown-in, and the R-value. Choose the R-value for your climate zone and code (see the ENERGY STAR table in the sources). For batts, pick the stud or joist spacing so the batt width fits.
Find the coverage. For batts, the square feet printed on the bag. For blown-in, the bags per 1,000 sq ft for your R-value from the bag’s coverage chart.
Add waste and divide. Add 5 to 10% to the area and divide by the coverage of one bag, or multiply by the bags per 1,000 sq ft ÷ 1,000. Round up to whole bags.
Check the thickness. For blown-in, make sure the settled depth is at least the chart’s minimum thickness for the R-value, as well as using the bags.

Worked examples

Project	Result
60 ft of 2 × 4 wall, 8 ft high, R-13 batts for studs 16 in on center, typical bag	480 sq ft + 5% → 5 bags
120 ft of 2 × 6 wall, 8 ft high, less two doors and six windows, R-21 batts for studs 24 in on center, 10% extra	847.98 sq ft + 10% → 11 bags
40 × 30 ft attic floor, R-30 batts between joists 16 in on center	1,200 sq ft + 5% → 24 bags
The first wall with R-13 bags that say 88.5 sq ft on the label	480 sq ft + 5% → 6 bags
40 × 25 ft attic blown-in with AttiCat to R-38 (13.5 in settled)	1,000 sq ft + 5% → 20 bags
30 × 40 ft attic blown-in with AttiCat to R-49 (17 in settled)	1,200 sq ft + 5% → 32 bags
The R-38 attic with a product whose label says 22 bags per 1,000 sq ft	1,000 sq ft + 5% → 24 bags

Frequently asked questions

How many bags of insulation do I need?: Divide the area, plus a little extra, by the square feet in one bag. A 60 ft run of 8 ft wall is 480 sq ft; with 5% extra that is 504 sq ft, and a typical 106.56 sq ft bag of R-13 batts gives 5 bags. The sq ft per bag changes with the product, so use the figure on the bag you are buying. Blown-in is counted by the chart for its R-value instead: bags per 1,000 sq ft × the area ÷ 1,000.
Do I subtract the studs or joists?: No. A batt’s printed coverage is its own area, which includes the strip it covers over the framing, and the calculator uses the area of the wall or attic as measured. Subtract doors, windows and hatches, since you do not insulate those. Cutting around wires, boxes and pipes is what the waste allowance is for.
Should I use 15 in or 23 in batts?: Studs 16 in on center leave a 14.5 in gap, so wall batts are made 15 in wide for a snug friction fit; studs 24 in on center take a 23 in batt. The R-30 and R-38 attic batts that are 48 in long are 16 and 24 in wide for joists at 16 and 24 in on center. Pick the spacing here and the calculator uses the typical bag for that width.
How many square feet are in a bag of batts?: It depends on the R-value, width, length and how many batts the pack holds. For Owens Corning EcoTouch PINK as listed by distributors, a bag of R-13 for 16 in studs is 106.56 sq ft, R-19 is 77.5 sq ft and R-30 is 53.33 sq ft, and the thicker the batt, the fewer sq ft in a bag. These are typical figures, not a standard: the bag in your hand is the truth. Type its number into the sq ft per bag field.
How are blown-in insulation bags counted?: From the manufacturer’s coverage chart: it lists, for each R-value, the bags per 1,000 sq ft and the minimum thickness once the insulation has settled. For AttiCat to reach R-38 the chart says 19 bags per 1,000 sq ft and 13.5 in; a 40 × 25 ft attic (1,000 sq ft) needs 19 bags, or 20 with 5% extra. R-49 is 25 bags per 1,000 sq ft and R-60 is 31.5.
Why does the thickness matter as well as the bags?: The R-value on the chart is only reached when you install the required number of bags and the insulation is at least the minimum thickness, which is why the chart lists both. Spreading the bags over more area than the chart allows gives a thinner, lower-R layer. Staple depth markers to the rafters or joists so you can check the depth as you blow.
My bag’s coverage chart does not match AttiCat. What do I do?: Use yours. Coverage charts differ by product (fiberglass or cellulose) and density. Find your target R-value on your bag’s chart, copy the bags per 1,000 sq ft into the bags per 1000 sq ft field, and the bag count follows. For example, 22 bags per 1,000 sq ft over a 40 × 25 ft attic is 24 bags with 5% extra, against 20 for the AttiCat chart.
What R-value should I aim for?: It depends on your climate zone, the part of the house and what you already have. The U.S. Department of Energy publishes a table of recommended R-values for attics, floors and walls by climate zone, which ENERGY STAR hosts as Recommended Home Insulation R-Values (linked in the sources). Check that table and your local code for your zone; this page does not copy the numbers.
How much waste should I allow?: The 5% and 10% choices are rules of thumb, not manufacturer figures. 5% suits open walls and attic floors with few cuts; 10% suits walls with many cuts around windows, wiring and boxes, or an attic with lots of obstructions. Bags only come whole, so the rounding up adds some more.