Estimate batt and roll insulation by area and R-value for walls, ceilings and floors.
Quick answer: Insulation is estimated by area and chosen by R-value: R-13 to R-15 for 2×4 walls, R-19 to R-21 for 2×6 walls, and R-30 to R-49 for ceilings, depending on your climate zone. A 1,000 sq ft attic at R-30 needs about 1,050 to 1,100 sq ft of product once you allow for joist bays and cuts.
How do you want to enter the area?
sq ft
Insulation type
%
Cutting waste is normally 5–10%; diagonal layouts need 15%.
$
Batts are usually priced per bag or per sq ft; blown-in per bag with blower rental often included.
Insulation to order
3
bags of batts
Estimated material cost
$165
200 sq ft + 5% waste = 210 sq ft
Also on the shopping list
Vapour barrier1 × 1000 sq ft rolls (if your assembly needs one)
Insulation staples2 boxes
Safetygloves, long sleeves and eye protection for mineral wool or fibreglass
Ordering one extra bag beats a mid-job shortage: dye lots, tile calibre and wallpaper print runs change between batches, so a later top-up may not match what you already installed.
Every coverage figure here is typical, not exact: box sizes, sheet sizes, roll widths and bag yields change between brands. Check the label on the product you actually buy and round up — a second trip costs more than a spare box.
Core facts
2×4 wall
R-13 to R-15 batts, typical
2×6 wall
R-19 to R-21 batts, typical
Ceilings
R-30 to R-49 by climate zone
Coverage per bag
varies by R-value and width, read the bag
What is Insulation Calculator?
Insulation slows heat moving through a surface, and its performance is rated by R-value: higher numbers resist more heat flow. Batts and rolls are sized to fit standard framing, 15 inch widths for 16 inch stud spacing and 23 inch for 24 inch spacing, and their thickness is set by the cavity depth. A 2×4 wall takes R-13 or R-15, while a 2×6 wall takes R-19 or R-21. Estimating is mostly an area calculation: measure the surfaces you are insulating, allow for joist bays, studs and cuts, and buy coverage by the bag, where the square footage printed on the label tells you how far it goes.
Common uses for Insulation Calculator
Work out how many bags an attic re-insulation needs
Choose an R-value for your climate zone and cavity depth
Estimate batts for a basement or garage wall
Compare batt coverage costs against loose-fill blown-in insulation
Price a DIY insulation job from area and R-value
Area first, then R-value
Every insulation estimate starts with square footage: wall length times height, attic length times width, floor area, minus large openings. Multiply by the number of layers you need for the target R-value if you are stacking batts. The coverage published on the bag converts that total into bags. Getting the area right matters more than agonizing over one step of R-value.
Thickness is set by the cavity
Batts only perform at their rated R-value when they fill the cavity without being compressed. A 2×4 wall has about 3.5 inches of depth and takes R-13 or R-15, and a 2×6 wall takes R-19 or R-21. Forcing a thicker batt in flattens it and wastes money. Where you need more, add rigid foam or a continuous layer outside the framing.
Air sealing beats adding R-value
Insulation slows heat conduction, but it does not stop air movement. Gaps around wiring, plumbing, sill plates and attic hatches can leak more heat than an under-insulated wall loses. Seal those first with caulk and spray foam, then insulate, and do it before the cold season arrives. The same budget spent in that order usually produces a noticeably warmer house for less money than insulation alone.
Frequently Asked Questions
What R-value do I need?
It depends on where you live and what you are insulating. The US Department of Energy publishes recommended levels by climate zone, commonly R-13 to R-15 for 2×4 walls, R-19 to R-21 for 2×6 walls, R-30 to R-60 for attics and R-13 to R-30 for floors. Colder zones need the higher end of each range.
How much area does a bag of insulation cover?
The label states the square footage per bag, and it varies widely by R-value and batt width. A higher R-value means a thicker batt, so fewer square feet per bag. Bags are usually sold in bundles covering a stated area, so divide your total area by the coverage printed on the bag.
Can I add insulation over existing insulation?
Yes for attics, where you can lay unfaced batts or blown insulation across the top of existing material, ideally running perpendicular to the joists so the framing gets covered. Do not compress the old insulation. In walls, adding insulation usually means opening the wall or having it blown in through small drilled holes.
Does compressing insulation reduce its R-value?
Yes. R-value depends on trapped air, and squashing a batt into a smaller cavity reduces the air it can hold. A thick batt crammed into a shallow space performs closer to the thinner batt it resembles. Match batt thickness to cavity depth, and never pack insulation tightly around wires, pipes or recessed light fixtures.
Should I use batts or blown-in insulation?
Batts suit open walls, floors and joist bays where framing is regular and visible, and they are easy to install yourself. Blown-in insulation fills irregular spaces, covers attic joists evenly and is faster over large areas, but it needs a machine and is messier. For a whole attic, blown-in often wins on coverage per dollar.