Property Repair Calculators

Insulation Calculator

ENERGY STAR recommends R-30 to R-60 for an uninsulated attic, depending on climate zone. [1] Choose your zone and where you are insulating to fill in the recommended R-value, then measure the area to count bags of blown-in insulation or packages of batts from manufacturer coverage charts.

Results

Bags of blown-in insulation

Owens Corning AttiCat, 27.5 lb bags, at R-60

Area: 1,000 sq ft
Target R-value: R-60
Chart R-value used: R-60
Minimum settled depth: 20.5 in
Bags per 1,000 sq ft: 31.5

Install both the bag count and at least the minimum depth; the chart R-value needs both. The AttiCat chart applies to that product and machine only. Other brands have their own bag charts.

How this was calculated

Area = 1,000 sq ft
Target R-60 → chart row R-60 (lowest charted value at or above your target)
Bags = 1,000 ÷ 1,000 × 31.5 = 31.5 → 32
Minimum settled depth at R-60: 20.5 in

Worked example

A 40 × 25 ft (1,000 sq ft) uninsulated attic in climate zone 4A, insulated with Owens Corning AttiCat blown-in fiberglass.

Target:  ENERGY STAR, zone 4A/4B, uninsulated attic = R-60
Chart:   AttiCat R-60 = 31.5 bags per 1,000 sq ft, 20.5 in minimum settled depth
Bags:    1,000 ÷ 1,000 × 31.5 = 31.5 → 32 bags

How the formula works

target R      = ENERGY STAR table for your zone and location (editable)
chart row     = lowest R-value on the product chart at or above the target
blown-in bags = area ÷ 1,000 × bags per 1,000 sq ft, rounded up
batt packages = area ÷ sq ft per package, rounded up

If your target falls between chart rows, the calculator uses the next higher row so you don’t under-insulate. For blown-in, the chart R-value needs both the bag count and the minimum settled depth. [2]

Limitations

ENERGY STAR’s table is for adding insulation to existing wood-framed homes and is based on the 2021 IECC. Your local code may require different values for new work or a permit.
Coverage comes from one product per type (Owens Corning AttiCat, Johns Manville kraft-faced batts). Other products have different bag and package coverage.
Above-ground walls: ENERGY STAR recommends blowing insulation into empty cavities and adding insulative sheathing when siding is replaced, rather than a batt R-value. This calculator does not size wall retrofits.
Batts must fit the cavity depth. A batt thicker than the framing gets compressed and loses R-value.
Air sealing, vents, baffles, and insulation dams around recessed lights and chimneys are not included, and insulation must keep required clearances from heat sources.

Common scenarios

Topping up an attic with 3–4 in already: choose “Attic, already has 3–4 in.” ENERGY STAR’s values for that case are the amount to add.
Replacing insulation after a roof leak or water loss: wet insulation loses R-value and can hold moisture against framing. Measure only the removed area, and fix the leak and dry the framing first.
Floor over a crawlspace or garage: choose “Floor over unheated space” and use batts sized to the joist depth.
Not sure of your zone: the ENERGY STAR page has a map. Most of the Gulf Coast is zones 1–2; the northern states are 5–7.

Common questions

What R-value do I need in my attic?

ENERGY STAR recommends R-30 in zone 1, R-49 in zones 2–3, and R-60 in zones 4–8 for an uninsulated attic. If you already have 3–4 in, it recommends adding R-25 to R-49 depending on zone.

How many bags of blown-in insulation do I need?

Use the coverage chart on the bag. For Owens Corning AttiCat, R-49 takes 25 bags per 1,000 sq ft at a minimum settled depth of 17 in, and R-60 takes 31.5 bags.

Batts or blown-in for an attic?

Both work. Blown-in fills around obstructions and irregular joists more easily; batts suit open, regularly spaced framing and floors. The calculator counts either.

What climate zone am I in?

ENERGY STAR groups zones as 1, 2, 3, 4A or 4B, 4C, 5, or 6, 7 or 8. Use the map on the ENERGY STAR R-value page to find yours.

Does this include the cost of insulation?

No. This page is quantity only. Prices vary by product, region, and whether you install it yourself.

Sources and methodology

Recommended R-values come from ENERGY STAR. Coverage figures are for specific manufacturer products, used as starting points. This page is quantity only: it uses no prices.

[1] ENERGY STAR — Recommended Home Insulation R-Values. Retrieved 2026-09-25. Recommended R-values by climate zone for attics and floors, and the basement/crawlspace wall notes. ENERGY STAR says its guidance is based on the 2021 International Energy Conservation Code (IECC) Residential Provisions, Chapter 4, Table R402.1.3. For above-ground walls it recommends blowing insulation into empty cavities and adding insulative sheathing when siding is replaced, rather than a batt R-value.
[2] Owens Corning — AttiCat PINK Blown-In Insulation product data sheet. Retrieved 2026-09-25. AttiCat chart (27.5 lb bag): bags per 1,000 sq ft and minimum settled thickness for R-13 to R-60.
[3] Johns Manville — Fiberglass Manufacturers Fact Sheet (BID-380 12/19). Retrieved 2026-09-25. Kraft-faced batt sizes, thickness, and sq ft per bag. JM notes R-19 compressed into a 2×6 wall (5½ in cavity) gives R-17 to R-18.

This tool provides an educational estimate only. Insurance companies, contractors, and building officials may calculate these figures differently depending on policy language, property condition, local pricing, and applicable codes.

Disclaimer: Calculators and information on this site are provided for educational and estimating purposes only. Results do not determine insurance coverage, claim payments, repair requirements, or professional recommendations.