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How Much Insulation for a 600 Sq Ft Attic?

A 600 sq ft attic going from R-11 to R-49 needs about 15.2 inches of blown fiberglass, which is 760 cubic feet of insulation. The tables cover other starting R-values, targets and insulation types.

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Roughly: 3.5 in of fiberglass batt is R-11 and 6 in is about R-19.

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Example job shown. Change the numbers to match yours.

Insulation to add
15.2 inches
R-38 more to reach R-49
Volume of insulation
760 ft³
R-value to add
38 R
Attic floor area
600 ft²
  • Loose-fill insulation settles and its R-value per inch varies with the product, so use the coverage chart on the bag for the exact bag count. Air-seal gaps and bypasses before insulating, keep insulation off the soffit vents (use baffles), and keep it clear of recessed lights unless they are IC-rated.

Before you buy: round up to whole packs, check the size printed on the label, and add a little spare. Your supplier has the final say.

Insulation depth to add, by current and target R-value

Depths are for blown fiberglass at R-2.5 per inch, in a 600 sq ft attic. Loose-fill settles, so add a small allowance, and keep it clear of the soffit vents with baffles.

You have nowTo R-30To R-38To R-49To R-60
None (bare floor)12.0 in15.2 in19.6 in24.0 in
R-117.6 in10.8 in15.2 in19.6 in
R-194.4 in7.6 in12.0 in16.4 in
R-30none needed3.2 in7.6 in12.0 in

Which insulation, going from R-11 to R-49

The R-value you add is the same, but the thickness and the volume change with the type of insulation. Spray foam is much thinner for the same R-value but costs more.

TypeR per inchDepth to addVolume to buy
Blown fiberglassR-2.515.2 in760 cu ft
Fiberglass battsR-3.211.9 in594 cu ft
Blown celluloseR-3.510.9 in543 cu ft
Open-cell spray foamR-3.710.3 in514 cu ft
Closed-cell spray foamR-6.55.8 in292 cu ft

Use the attic insulation calculator for your own attic, and read how much attic insulation you need for climate-zone targets. Seal air leaks first, and check attic ventilation before you add more.

Want to change anything else? The calculator above is the full Attic Insulation Calculator: edit any number and the results update instantly.

Tools & materials for this project

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Blown-in fiberglass insulationFiberglass batts (R-30)Attic bafflesSpray foam sealantRespirator mask

Frequently asked questions

How many inches of insulation does a 600 sq ft attic need?

From R-11 to R-49 with blown fiberglass (R-2.5 per inch) you add about 15.2 inches. From a bare floor it is 19.6 inches. The depth is the same for any attic size: the area only changes how much material you buy.

How much insulation do I need to buy for a 600 sq ft attic?

About 760 cubic feet of blown fiberglass to go from R-11 to R-49. Check the coverage chart on the bag: it lists bags needed at each depth, and settling means you should buy a few extra.

Is R-38 enough for a 600 sq ft attic?

R-38 is a common recommendation for milder climates, and from R-11 it means adding 10.8 inches of blown fiberglass (540 cu ft). Cold climates are better at R-49 to R-60. Check your climate zone in the calculator.

Related sizes and guides

800 sq ft atticR-11 to R-49: 1,013 cu ft1,000 sq ft atticR-11 to R-49: 1,267 cu ftHow much attic insulation do I need?GuideAttic Ventilation CalculatorKeep the air moving

Related sizes

1,500 sq ft atticR-11 to R-49: 1,900 cu ft2,000 sq ft atticR-11 to R-49: 2,533 cu ft1,200 sq ft atticR-11 to R-49: 1,520 cu ft1,800 sq ft atticR-11 to R-49: 2,280 cu ft2,500 sq ft atticR-11 to R-49: 3,167 cu ft

Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.