How many bags of insulation do I need?

Divide the area you are insulating by the coverage one bag gives at your chosen thickness, then round up. Coverage is printed on the bag and falls as the target depth rises, so it is the number that drives the answer and it is editable here. Enter the area and the bag coverage and the tool counts the bags.

Does this tell me what R-value to use?

No — and that is deliberate. The required R-value for a wall, ceiling or floor is set by your building code and climate zone, not by a calculator, so this tool never suggests one. You decide the R-value from your code, read the coverage the bag gives at that value, and enter it here. The arithmetic is all this does.

How is blown-in coverage different from batts?

Blown-in loose fill is sold by the bag, and the bag states how many square feet it covers at each settled thickness — that is the coverage figure to enter. Batts are sold by the bundle with a stated square footage instead; enter that bundle coverage in the same field and the count still works.

Insulation calculator

This divides the area you enter by the coverage you enter — nothing more. It does not set an R-value, judge whether a cavity is deep enough, or account for framing and voids, all of which are governed by your building code. Follow that code and the product's own instructions.

Enter the area you are insulating and the coverage one bag gives at your target thickness. The tool totals the area, adds a small margin for settling and off-ratio spots, divides by the bag coverage and rounds up to whole bags.

Worked example

An attic 30 ft × 20 ft is 600 square feet. If a bag of loose fill covers 40 sq ft at your chosen depth, that is 600 ÷ 40 = 15 bags before waste. Add 5% for settling and rounding and you are buying 16 bags. Aim for a deeper R-value and the coverage per bag drops, so the count climbs.

The formula

bags = (area × (1 + waste)) ÷ coverage per bag, rounded up

The coverage already carries the thickness inside it — a bag that covers 40 sq ft deep enough for a high R-value covers far more when spread thin. That is why the tool asks for coverage rather than depth: it keeps the one variable that changes with your code requirement in your hands.

Questions

How many bags of insulation do I need?: Divide the area you are insulating by the coverage one bag gives at your chosen thickness, then round up. Coverage is printed on the bag and falls as the target depth rises, so it is the number that drives the answer and it is editable here. Enter the area and the bag coverage and the tool counts the bags.
Does this tell me what R-value to use?: No — and that is deliberate. The required R-value for a wall, ceiling or floor is set by your building code and climate zone, not by a calculator, so this tool never suggests one. You decide the R-value from your code, read the coverage the bag gives at that value, and enter it here. The arithmetic is all this does.
How is blown-in coverage different from batts?: Blown-in loose fill is sold by the bag, and the bag states how many square feet it covers at each settled thickness — that is the coverage figure to enter. Batts are sold by the bundle with a stated square footage instead; enter that bundle coverage in the same field and the count still works.

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