Calculators
Insulation Calculator
Estimate insulation batts and bags to buy from wall size, batt coverage, and waste allowance locally in your browser.
Enter the wall size and a single insulation batt's coverage in feet to estimate how many batts to buy, including a waste allowance for cuts, framing, outlets, and breakage. The calculation runs locally in your browser; your values are not uploaded or stored.
Enter batt dimensions in the same unit as the wall; for example, a 93 by 15 inch batt is about 7.75 by 1.25 ft. This estimate covers one flat wall face and ignores doors, windows, studs, wiring, and plumbing cutouts, so measure each face separately and add extra waste for obstructed walls. Check your supplier because batt sizes and bag counts vary by product and R-value. This insulation estimate is a planning guide, not a purchase guarantee.
Find how many insulation batts to buy without uploading anything.
Enter the wall length and height plus a single insulation batt length and width, an optional batts-per-bag count, and a waste allowance to see the wall area, batt count, and rounded-up bag count. Everything runs locally in your browser, so your values are not uploaded or stored.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
What does the insulation calculator show?
Enter the wall length and height, a single insulation batt length and width in the same unit, an optional batts-per-bag count, and a waste allowance. The calculator returns the wall area, the batt coverage, and the batt count with waste rounded up, plus the bag count when batts per bag is given, with the calculation shown. For example, a 20 by 8 ft wall with 8 by 1.25 ft batts and 10% waste needs about 18 batts, so buy 2 bags at 10 batts per bag.
Which formula does the insulation calculator use?
It uses wall area = wall length x wall height, batt area = batt length x batt width, then batts = wall area / batt area x (1 + waste percent / 100) rounded up, and bags = batts / batts per bag rounded up. Use the same length unit for the wall and the batt; for example, a 93 by 15 inch batt is about 7.75 by 1.25 ft. The estimate covers one flat wall face and ignores doors, windows, studs, and cutouts, so measure each face separately.
Which inputs are accepted?
Enter a wall length, wall height, batt length, and batt width greater than zero through 1000000000, an optional whole-number batts-per-bag count from 1 to 1000000000, and a waste allowance from 0 to 100 percent (blank means 10). Decimal dimensions are accepted. Zero, negative numbers, non-numeric text, and out-of-range values show a clear error instead of a result.
Does the insulation calculator upload my values?
No. The whole calculation runs locally in your browser. Your wall and batt dimensions, bag count, and waste allowance are not uploaded, stored, or sent to a server.