RenoSheets
ENFR

Insulation Calculator

Enter area and target R-value for batt or blown-in bag count — plus vapor barrier and safety gear.

Input
Wall / ceiling section 1
Application
Target R-value
Stud spacing
Waste allowance10%

108 sq ft net → 119 sq ft with waste → 3 bags

You'll need
3 bags
of R-19 batt insulation

108 sq ft · R-19 · wall-batts · 10% waste.

Materials list

Vapor barrier0 rollsoptional
Recommended in cold climates — check the option above to add
Safety glasses + N95 mask1 set
Fiberglass and mineral wool irritate skin, eyes and lungs — PPE is not optional
Work gloves + long sleeves1 pair
Fiberglass fibres cause skin irritation — cover all skin when handling batts

Tools you'll want

Buy-once items — skip any you already own.

Staple gun + staples
Heavy-duty stapler to fasten kraft-faced batts to studs
Utility knife + blades
Score and snap kraft-faced batts cleanly. Keep extra blades on hand.

Where to buy (optional)

Happy with your list? Tap any item below to open it at a retailer. These are affiliate links that support the site at no extra cost — but shop wherever you like.

Estimates only — verify quantities before buying.

How to calculate insulation bags

Batt insulation bags cover a fixed area at a given R-value; blown-in coverage is listed on each bag:

— Batts (e.g. R-19, 16 in o.c.):
  bags = ceil(area with waste / coverage per bag)
  coverage: ~38–40 sq ft per bag (varies by product)

— Blown-in (e.g. R-38 at 16 bags/1000 sq ft):
  bags = ceil(area with waste / 1000 * bags_per_1000)

Coverage values are calibrated to published Owens Corning and CertainTeed SKUs. Always verify with the coverage chart on the actual bag — coverage varies by manufacturer.

Common mistakes

  • Compressing batts to fit — compression reduces R-value. If it doesn't fit without force, trim it.
  • Leaving air gaps around wires, pipes and outlets — seal all penetrations with caulk or foam before installing batts.
  • Installing vapor barrier on the wrong side — always on the warm side (interior in cold climates).
  • Skipping PPE — fiberglass fibres cause skin, eye and lung irritation. Always wear gloves, long sleeves, safety glasses and an N95 mask.

Frequently asked questions

What R-value do I need for exterior walls?+

R-13 to R-15 for 2×4 walls; R-19 to R-21 for 2×6 walls. The International Energy Conservation Code (IECC) requires R-20 for 2×6 walls in most cold-climate zones and R-13 for warmer zones. Check your local building code for the exact requirement for your climate zone.

What R-value do I need for an attic?+

Most climate zones require R-38 to R-60 for attic insulation. IECC Climate Zone 5 (including much of the northern US and Canada) typically requires R-49. Climate Zones 1–3 in the south may only require R-30. Adding more insulation than the minimum almost always has a positive ROI in energy savings.

How many bags of blown-in insulation do I need for R-38 in a 500 sq ft attic?+

For R-38, plan on about 16 bags per 1000 sq ft of attic floor area. A 500 sq ft attic needs about 8 bags. The exact count depends on the brand — check the coverage chart printed on every bag for the settled depth and bag count at your target R-value.

What is the difference between R-13 and R-15 insulation?+

R-13 and R-15 batts are both designed for 2×4 walls at 16 in on-center. R-15 uses a denser formulation — either high-density fiberglass or rockwool (mineral wool) — to pack more R-value into the same 3.5 in cavity. Rockwool R-15 also provides better sound damping and fire resistance than fiberglass.

Do I need a vapor barrier with insulation?+

In cold climates (roughly Zone 5 and colder), a 6-mil poly vapor barrier on the warm side of wall insulation is required by code. In mixed climates (Zone 3–4), smart vapor retarders or vapor-permeable barriers are often better. In hot climates (Zone 1–2), you generally do not need a vapor barrier. Always check local building code.

Can I rent an insulation blower for blown-in insulation?+

Yes — most big-box home improvement stores lend or rent a blower machine when you purchase a minimum number of bags (typically 10–20). Ask at the building materials desk. Renting an insulation blower separately costs about $60–100 per day. The machine is much faster than hand-packing batts for large attic areas.

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Reviewed by the RenoSheets team for calculation accuracy. Method: area with waste divided by coverage per bag; blown-in from bags-per-1000-sq-ft curves. Last updated 2026-05-24. Estimates only — verify bag coverage on the product label before purchasing.