How the insulation calculation works

The calculator finds the surface area, deducts any openings, adds your waste allowance and divides the result by the coverage supplied in one pack.

Walls, floors and ceilings

For a rectangular wall use width × height. For a floor or ceiling use length × width. Calculate separate areas individually if the surfaces use different insulation products or thicknesses.

This tool estimates quantities only. Required insulation type, thickness, fire performance and thermal performance depend on the construction and applicable building requirements.

Frequently asked questions

Should I deduct windows and doors?

For large openings, yes. Small deductions can be left in as part of the waste allowance.

Why do pack coverage figures vary?

Coverage depends on the product dimensions, number of pieces in a pack and insulation thickness.

Using pack coverage correctly

The pack count is based on surface area rather than insulation volume, so enter the coverage figure for the exact thickness and product you intend to buy. A manufacturer may sell the same insulation range in several thicknesses with different square-metre coverage per pack. Using the wrong pack coverage can materially change the order quantity even when the wall or ceiling area is measured correctly.

Allow for framing and awkward cuts

Regular stud or joist bays can make efficient use of rolls or slabs that match the spacing. Narrow bays, edges, loft hatches and service penetrations create more offcuts. The waste allowance is intended for those normal cutting losses; it should not be used to compensate for an uncertain measured area.

Quantity is not thermal design

This calculator estimates how many packs cover a surface. It does not determine the insulation thickness, U-value, condensation risk, ventilation strategy or compliance of a wall, roof or floor build-up. Those depend on the construction and project requirements. Once the required insulation specification is known, use its actual pack coverage here and check the manufacturer's installation guidance before ordering.