Insulation Calculator
Calculate how many cubic meters of insulation you need for a wall, roof or floor, based on length, width and thickness.
How to use the insulation calculator
- Enter the length and width (or height) of the surface to be insulated.
- Enter the desired insulation thickness — common for exterior walls is 150–200 mm, for interior walls 70–100 mm.
- The calculator shows the volume in cubic meters, which you can compare to the coverage stated on the insulation product.
How the insulation amount is calculated
The volume is area times thickness, once the thickness is converted from millimeters to meters:
Insulation products are normally sold in packs labeled with how many square meters they cover at a given thickness — check the packaging for the exact thickness you're using, since pack sizes vary a lot between products and manufacturers.
Insulation only works when it sits tight
Mineral wool insulates by holding air still in millions of tiny pockets. Compress it and the insulating value falls; leave gaps around the edges and air currents form that carry heat straight past the insulation. Batts should therefore be cut a few millimetres wider than the stud spacing, so they grip lightly into place without being crammed in.
Vapour and wind barriers are part of the same system. Without a sealed vapour barrier on the warm side, humid indoor air migrates into the construction and condenses where it is cold, which both reduces insulating performance and causes rot damage over time. This calculator works out the quantity of insulation — barrier layers, taped joints and any battening come in addition.
Frequently asked questions
How thick should the insulation be?
It depends on the building part and climate zone. Exterior walls are often insulated with 150–250 mm, roofs with 300–400 mm, and interior walls (sound only) with 70–100 mm. Check your local building code for minimum requirements.
Can I use the calculator for multiple layers of insulation?
Yes, calculate each layer separately with the correct thickness for that layer, then add the volumes together.