Insulation Calculator

Pick the insulation type and the R-value you are aiming for. This returns how deep it has to be, and how much material that is for your square footage.

Your numbers

Insulation typeR-value per inch of thickness.Target R-valueUS DOE recommends R-49 to R-60 for attics in most of the country, R-13 to R-21 for walls.Existing R-valueAdding on top of what is already there? Put its R-value here.Area to insulate(sq ft)Attic floor, or total wall area. Drives the bag count, not the depth.Coverage per bag(sq ft)At the depth you need. Printed on the bag as a coverage chart.

Result

Depth required

19.6

inches

Bags or bundles: 30bags
R-value to add: 49R
Finished R-value: 49R
Area covered: 1,200sq ft
Board feet of foamHow spray foam is quoted: 23,520bd ft

How this is calculated

R-value to add = target R − existing R.
Depth = R-value to add ÷ R-value per inch of the material.
Bags = area ÷ coverage per bag at that depth.
Board feet = area × depth in inches - the unit spray foam is priced in.

Before you order

Coverage per bag is not a constant. Every blown-insulation bag has a chart on it giving coverage at each depth, and deeper means fewer square feet per bag - use the number for YOUR depth.
Batts only reach their rated R-value if they fill the cavity without being compressed. An R-19 batt squashed into a 2x4 wall does not perform as R-19.
Do not bury recessed lights, bath fans or a chimney without checking clearances first. Non-IC-rated fixtures are a fire risk when covered.
Attic ventilation has to keep working. Baffles at the eaves stop blown insulation from blocking the soffit vents.

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