This calculator turns a measured wall, ceiling, or floor area into whole rolls or packs of batt insulation using the product's stated coverage. Use it once the required thermal value, thickness, and framing width have been selected under local rules. It does not choose an R-value or U-value, calculate heat loss, cover blown-in or spray systems, or include membranes, fixings, ventilation work, PPE, and labour. US mode uses square feet and common R-value products, while UK mode uses square metres and metric pack coverage; always replace the default with the exact label figure. Give the area and assembly details to the insulation merchant or installer so they can confirm product suitability, pack coverage, number of layers, and vapour-control requirements.
How this is calculated
Roll count is net area plus waste, divided by the coverage printed on the packaging. Standard US batts often cover about 40 ft² per roll; UK rolls vary more — change the assumption to match your product.
This does not pick an R-value for you. Buy the thickness that meets your code or target; the calculator only handles how many rolls that thickness requires.
Measure each wall or ceiling plane separately, then add the areas. Door and window openings are often left in the gross area for batts because you still cut and fit around the opening — only subtract large openings if your installer works that way.
Attic and floor jobs may need two layers or a different product (blown cellulose, rigid board). If the label coverage assumes a single batt pass, do not force this roll math onto a blown-in quote.