Insulation Calculator
Enter your area to get the insulation packs you need, plus an estimated cost. Waste is included.
Insulation needed
Estimated cost
How to calculate insulation
Insulation is sold by the pack, and each pack covers a fixed area. Find the area, add waste for cuts around joists and wires, then divide by the coverage per pack and round up.
Formula: packs = area (sq ft) × (1 + waste %) ÷ coverage per pack, rounded up
Worked example: 20 ft × 15 ft area
Area = 20 × 15 = 300 sq ft. Add 10% waste: 330 sq ft. At 100 sq ft per pack: 330 ÷ 100 = 3.3, rounded up to 4 packs.
Check the label
Coverage per pack varies a lot by product and R-value, so read the pack label and enter that number. Using a guessed number is the most common cause of under-ordering.
Common sizes
Cost tips
Prices on this page are editable estimates, not quotes. Get 2 to 3 local quotes before you buy, and ask if delivery is included. Delivery, tax and waste can change the total a lot. Order a little extra for cuts and breakage, and confirm final quantities with your supplier or a qualified professional.
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Frequently asked questions
How much insulation do I need for a 20x15 area?
A 20 ft by 15 ft area needs 4 packs at 100 sq ft per pack, with 10% waste.
What coverage does a pack have?
It varies by product and R-value. Check the pack label and enter that number here.
What R-value should I use?
Attics usually need R-30 to R-60, walls R-13 to R-21, depending on climate. Check your local code.
How much waste should I add?
Add 10% for open areas and 15% for areas with many joists, wires and pipes.
Are the prices accurate?
Prices are editable estimates. The defaults are typical US figures, and your local price can be higher or lower.