Insulation calculator — estimate insulation quantities

Enter the area and insulation thickness to get the area including waste, the volume in cubic meters and how many packs to order — with typical pack contents pre-filled for each thickness.

m²
%

5% is often enough for stud bays — add more for sloped ceilings and angles.

m²

Typical value for the selected thickness — check your brand.

Number of packs
20 pcs
à 2.7 m²
Area incl. waste
52.5 m²
Volume
7.61 m³

Pack contents apply to typical 560/565 mm stud-bay batts and vary between brands and lambda classes — always check the product sheet before ordering.

The calculation is an estimate and does not replace engineering design or the supplier’s instructions. Always check against project documents, product data sheets and applicable codes.

How to estimate insulation quantities

The core calculation is simple: measure the area to insulate, add a waste margin and divide by the pack contents in m². For straight stud walls, 5% waste is often enough, since batts are sized to the stud spacing and friction-fit without cutting — for sloped ceilings, angles and lots of penetrations, plan for 10% or more.

Pack contents drop quickly with thickness: a pack of 45 mm batts covers almost 9 m², while a pack of 220 mm barely reaches 2 m². The calculator suggests a typical value for each thickness, but contents differ between brands and lambda classes — always check against the product sheet before ordering.

Choosing width, lambda class and thickness

Stud-bay batts are sold in widths matched to the stud spacing — for example 565 mm batts for 600 mm centers — so the batt springs out against the studs and fills the bay completely. That fit matters: gaps covering just a few percent of the area can measurably degrade the assembly’s thermal performance. The lambda class (33, 35, 37 or 39) tells you how well the material insulates: lower is better. Class 37 is the workhorse for stud walls, while class 33 earns its keep where space is tight and every millimeter counts, such as renovations where the wall can’t grow thicker.

How much insulation the building needs is set by your climate and energy code, not by any single assembly. As rough new-build reference points in cold climates: exterior walls often end up around 200–300 mm in total and attic floors at 400–500 mm. When retrofitting, the attic is almost always the best investment — large area, easy access and the biggest temperature difference. Just make sure ventilation and the vapor barrier are handled correctly so moisture isn’t trapped.

Frequently asked questions

How many square meters of insulation are in a pack?
It depends on the thickness — the thicker the batt, the fewer m² per pack. Typical values for stud-bay batts: 45 mm ≈ 8.7 m², 70 mm ≈ 5.6 m², 95 mm ≈ 4.1 m², 120 mm ≈ 3.3 m², 145 mm ≈ 2.7 m², 170 mm ≈ 2.3 m², 195 mm ≈ 2.0 m² and 220 mm ≈ 1.8 m² per pack. Always check your brand — contents vary.
What do lambda classes 33, 35, 37 and 39 mean?
The number is the thermal conductivity in mW/(m·K): class 33 conducts less heat than class 37 and insulates about 11% better at the same thickness. With class 33 you can reach the same U-value with a thinner construction — but the batts cost more per m², so it’s usually a trade-off between wall thickness and price.
What waste margin should I use for insulation?
For straight stud walls, 5% is often enough, since friction-fit batts are sized to the stud spacing and squeeze into place without cutting. For sloped ceilings, angled walls and areas with many penetrations, count on 10% or more.
How thick should wall and attic insulation be?
It depends on your climate and local energy code. In cold climates, well-insulated new-build exterior walls often carry around 200–300 mm of insulation in total, and attic floors 400–500 mm — the attic is usually the most cost-effective place to insulate since warm air rises. Exact thicknesses come out of the building’s energy calculation.
Stone wool or glass wool — which should I choose?
Both insulate equally well at the same lambda class. Stone wool withstands higher temperatures, damps sound slightly better in heavy constructions and is stiffer. Glass wool is lighter, compresses harder in the packs (less transport volume) and is often cheaper per m². Fire-rated assemblies often specify stone wool — follow the assembly’s approval documents.

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