How much insulation do I need?

Work out the area of the ceiling, wall, or floor to insulate, then divide by the coverage of one pack. The calculator does this and rounds up to whole packs. Coverage is printed on the pack and varies with the segment width and R-value.

What R-value do I need in New Zealand?

The Building Code sets minimum R-values that vary by climate zone and by whether it is a ceiling, wall, or floor. Ceilings need the highest. Check the current requirements for your area and choose a product that meets or beats them.

Should I allow for framing?

Insulation fits between the framing, so the actual segment area is a little less than the gross area. Buying to the gross area gives a small safety margin and covers offcuts, which is sensible.

Insulation Calculator

This calculator works out how many packs of insulation you need to buy for a ceiling, wall, or floor, so you can order the right amount rather than guessing and running short or paying for excess offcuts. Enter the area you are insulating in square metres and the coverage per pack, a figure printed on the packaging that varies with the segment width and the R-value of the product you choose. The calculator divides the area by the pack coverage and rounds up to a whole number of packs, since insulation comes in fixed pack sizes and you cannot buy part of one. It returns the packs to buy and the total area those packs actually cover, so you can see the spare coverage left for offcuts and awkward corners. Insulation fits between the framing rather than across the full gross area, so buying to the gross area you measured already builds in a small, sensible safety margin. Before you buy, check the R-value of the product meets the Building Code minimum for your climate zone and for whether you are insulating a ceiling, wall, or floor, since ceilings generally need the highest rating. Treat the packs figure as a practical shopping guide, and confirm exact quantities and R-value requirements with your supplier or installer before purchase, as pack sizes and coverage figures vary between brands and products.

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Area to insulate (m²)

Coverage per pack (m²)

0 packs

to buy

Area covered0 m²

Check the R-value meets the Building Code for your zone and the ceiling, wall, or floor.

How it works

Divide the area you are insulating by the coverage of one pack and round up to whole packs. Coverage depends on the segment width and the R-value of the product, so always use the figure on the pack you are buying.

Worked example

For an 80 square metre ceiling with packs that cover 8.16 square metres each, you need 80 divided by 8.16, which rounds up to 10 packs.

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