Free tool
Insulation Calculator
Enter the area you’re insulating and your product’s coverage — get the number of bags or bundles to buy, with openings subtracted and a waste factor built in. Free, no signup for the estimate.
Insulation needed
0 bags
- Gross area0 ft²
- Net area0 ft²
- With waste0 ft²
- Bags / bundles0
- Estimated cost—
Turn takeoffs into paid jobs
Get the free Job Pricing Kit — a printable pricing worksheet, the markup & margin cheat-sheet, and clean invoice + quote templates so the job you just measured becomes a professional quote. We’ll email it now.
Free PDF. No spam. Unsubscribe anytime.
✓ Check your inbox — the kit is on its way.
Or download it now (PDF)How to calculate insulation
Buying insulation comes down to one number — square feet of coverage — and then matching it to whatever the bag or bundle on the shelf actually covers. Get the area right, take out the openings you won’t insulate, and leave a little for trimming, and you walk out with the right count instead of a second trip.
1. Measure the area
For walls, multiply length × height; for a ceiling or attic, length × width. Add up each wall or bay and total the square footage. Measure the surface you’re actually covering — not the room’s floor area — so sloped or tall walls aren’t undercounted.
2. Subtract windows and doors
You don’t insulate a window or a door, so subtract those openings from the gross area. On a wall with a lot of windows this matters; on a blank attic it’s usually zero. Enter the total opening area and the calculator works from the net.
3. Add a waste factor
Batts get cut down around outlets, pipes, and odd-width bays, and some ends up as scrap. About 10% covers the offcuts so you’re not one piece short finishing a run. Blown-in is more forgiving, but a small allowance still keeps you from stopping partway.
4. Convert area to bags
Coverage per bag or bundle is printed on the package and varies by R-value and stud spacing — so pick your R-value first, then enter that product’s coverage. The calculator divides your net-plus-waste area by it and rounds up to whole bags.
Measuring the job is step one. Turning it into a priced, professional quote is faster inside CrewRivet. See the drywall calculator, the paint calculator, or the job pricing calculator.
Insulation calculator FAQ
- How much insulation do I need?
- Measure the area to cover — length × height for walls, length × width for a ceiling or attic — to get square feet. Subtract big openings like windows and doors, add about 10% for trimming and waste, then divide by the coverage printed on the bag or bundle you are buying. This calculator does all of it once you enter that coverage from the label.
- How many square feet does a bag of insulation cover?
- It depends entirely on the product, so the number is printed on the package. A bundle of faced batts commonly covers somewhere in the 40–110 sq ft range depending on R-value and stud spacing, and blown-in bags list coverage at a target depth. Enter the coverage from your label and the calculator turns your area straight into a bag count.
- What R-value do I need?
- R-value is set by your climate zone and where the insulation goes — attics usually want the highest R-value, walls less — and your local code lists the minimum for each assembly. This calculator sizes how many bags cover your area, not the R-value: pick the R-value first, then enter that product’s coverage so the bag count matches what you are actually installing.
- Why subtract openings and add waste?
- You do not insulate windows and doors, so subtracting them keeps you from over-buying on a wall full of glass. At the same time batts get trimmed around outlets, pipes, and odd bays, and some is wasted — a 10% allowance covers the offcuts so you are not one batt short at the end of the run.
- Is the calculator free?
- Yes — the live estimate is free with no email required. Enter your email only if you want the free Job Pricing Kit (pricing worksheet, markup cheat-sheet, and invoice + quote templates) sent to your inbox.