Free Insulation Calculator
Estimate insulation bags or bundles for walls and lofts from area and coverage. Free, fast, and works entirely in your browser with no sign-up required.
Updated
Insulation quantity
Printed on the packaging; falls as R-value rises.
Extra material for cuts, spillage and breakage.
Bags or bundles needed
16
bags
- Area to insulate
- 600ft²
- Stud/joist cavities
- 23cavities
How this is calculated
bags = (area + waste) ÷ coverage per bag, rounded up
- Coverage per bag falls as R-value rises — an R-13 bundle covers far more wall than R-30, so take the figure from the packaging.
- Batts are sized to fit 16 in or 24 in cavities; buy the width that matches your framing rather than cutting every piece.
- Compressing insulation to fit reduces its R-value; the stated coverage assumes it sits uncompressed.
Frequently Asked Questions
How does the Insulation Calculator work?
It applies the formula bags = (area + waste) ÷ coverage per bag, rounded up. Enter your measurements and the result updates instantly in your browser — nothing is uploaded and no sign-up is needed.
Why should I include a waste allowance?
Offcuts, spillage, breakage and an uneven sub-base all consume material that the raw geometry does not account for. The default allowance is deliberately modest; increase it for complex layouts, and remember that running short usually costs more in a second delivery than the surplus did.
Are the results exact?
They are a close estimate, not a guarantee. Coverage per bag falls as R-value rises — an R-13 bundle covers far more wall than R-30, so take the figure from the packaging. Real materials vary by supplier, moisture content and compaction, so confirm the rate with your supplier before placing a large order.
Is this tool free?
Yes, completely free with no registration. All calculations happen client-side in your browser.
Does it work on mobile?
Yes. The calculator is fully responsive and works on phones and tablets in any modern browser — useful when you are measuring on site.
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About the Insulation Calculator
The Insulation Calculator turns the area you are insulating into the number of bags or bundles required at your product's stated coverage. Enter your measurements and the result updates as you type — there is nothing to submit and nothing to wait for.
Everything runs in your browser. Nothing you enter is sent to a server, there is no sign-up, and there is no usage limit.
Who it's for
Anyone insulating a wall, loft or basement.
How the calculation works
bags = (area + waste) ÷ coverage per bag, rounded up
The result depends on a few standard constants, which are stated on the page rather than hidden:
- Coverage per bag falls as R-value rises — an R-13 bundle covers far more wall than R-30, so take the figure from the packaging.
- Batts are sized to fit 16 in or 24 in cavities; buy the width that matches your framing rather than cutting every piece.
- Compressing insulation to fit reduces its R-value; the stated coverage assumes it sits uncompressed.
Getting an accurate estimate
Measure twice. Small errors in a linear dimension compound, because material volume scales with two or three of them at once — a 6-inch error across a 20-foot run is over a cubic foot of material on a 4-inch pour.
Keep the waste allowance. The default is deliberately conservative: offcuts, spillage, uneven sub-base and breakage are all real, and running short mid-job usually costs more in a second delivery than the surplus did.
Round up when you order. Suppliers sell in fixed increments — quarter yards, whole bags, full boxes — so treat the figure here as the minimum you need rather than the exact amount to buy.