Insulation Calculator
Estimate whole packages from your product label. Supports wall, attic and loft projects with explicit coverage inputs and an optional ordering allowance.
How much insulation should I buy?
This calculator turns a measured area and the coverage on your chosen product into whole packs or bags. Choose batts/rolls or blown-in insulation. For a rectangular attic, multiply length by width. For walls, add wall lengths and multiply by height, then subtract appropriate openings. Sum separate sections before entering their area.
Batts and rolls
Net area = gross area − exclusions. Multiply net area by the number of full layers and your ordering allowance, divide by coverage per pack and round up. For 1,000 square feet, one layer, 5% extra and 100 square feet per pack, the order is 11 packs. At 40 each, the estimated cost is 440. Pack coverage is an example: replace it with your label.
Blown-in insulation
Use the manufacturer's maximum coverage per bag at the exact specified target R-value and application. The calculator ignores the layers field in this mode. Coverage already represents the complete installation described by that chart. Do not enter a batt pack's area or divide by a generic insulation density. Minimum bag weight, installed depth and settled depth must also satisfy the product instructions.
Why does R-value affect the bag count?
A higher target resistance can require more material per unit area. Owens Corning's Canadian ProPink L77 reference lists different coverage by R-value; its R-30 example is 77 square feet per bag. Using that figure for 1,000 square feet and zero extra gives 13 bags. Product versions and regional labels differ, so this is an arithmetic example rather than a universal preset.
Can I use this for a loft in the UK?
Yes. Choose square metres and enter coverage in square metres per pack. Changing units does not convert the existing values. For two complete layers of rolls, enter 2; for unequal areas at different thicknesses, estimate each layer separately. Keep costs in your own currency.
Does this choose thickness or calculate energy savings?
No. It estimates purchase quantity for a product and installation specification you already selected. It does not specify the required R-value, U-value, ventilation, fire clearances or insulation thickness. For topping up existing loose fill, use a manufacturer-approved top-up coverage chart rather than subtracting old depth from a new-installation rate.
What does the cost include?
Only whole packs or bags at your entered price. Delivery, equipment hire, protective equipment, installation and tax are separate. The extra percentage is an optional ordering contingency, not a change to the product's certified performance.
Reference: Owens Corning ProPink L77 coverage reference. Always use the current chart on the product you purchase.
Related: Drywall Calculator · Roof Square Footage Calculator
Reviewed 4 November 2026. Free, no signup. Inputs stay in your browser. Quantities are estimates; check measurements and product instructions before purchasing.