Insulation calculator
Insulating an attic, wall or floor? Enter the area and thickness and the calculator returns the number of packs, the volume and an approximate U-value – waste included. Save the result as a material list to take to the merchant.
Insulation calculator – quantity & U-value
Enter the area and insulation thickness and we work out the number of packs, the volume and an approximate U-value for the insulation layer. The default is mineral wool with lambda 0.036 W/mK.
An estimate. How many m² a pack covers depends on the thickness – the value is on the pack. The U-value applies only to the insulation layer; a correct U-value for the whole wall also accounts for studs, boards and thermal bridges. Boards 560 mm wide fit studs at c/c 600 mm.
This tool gives an estimate and is an aid – not a finished calculation. Always check the result against drawings, applicable regulations, supplier data and your professional experience before giving a binding price, ordering material or using the file. ByggExp is not responsible for decisions made solely on the basis of the tool.
Want help taking this further?
Briefly describe what you need and we’ll help you with a quote, material and next steps – free of charge. Only the contact field is required.
What the calculator works out
- Need: the area plus waste (m²).
- Packs: the need divided by m² per pack.
- Volume: area × thickness (m³).
- U-value (approx.): lambda ÷ thickness – for the insulation layer only.
Thickness, lambda and U-value
The same pack covers fewer m² the thicker the insulation you choose. Thicker layers and a lower lambda give a lower U-value (better). Roughly: 10 cm of mineral wool ≈ U 0.4, 20 cm ≈ 0.2 and 40 cm ≈ 0.1 W/m²K. Check what thickness your structure (attic, wall, floor) requires before ordering.
Studs, board width and thermal bridges
Insulation boards of 560 mm fit studs at c/c 600 mm. Consider laying the insulation in two crossing layers so the studs don’t form continuous thermal bridges – in practice this gives a noticeably better wall than the U-value of the insulation layer alone suggests.
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Frequently asked questions
- How much insulation is needed?
- Enter the area and the calculator adds your waste allowance (5% by default), then divides the total by how many m² one pack covers. You get the volume in m³ and the number of packs to order.
- What do lambda and U-value mean?
- Lambda (W/mK) is the material’s thermal conductivity – mineral wool is about 0.033–0.037. The U-value describes how much heat the construction lets through, and lower is better.
- Does the calculator’s U-value cover the whole wall?
- No, it applies to the insulation layer only (U ≈ lambda ÷ thickness). A correct whole-wall value also counts the studs, boards and thermal bridges, which let through more heat than the insulation itself.
- Which c/c should the studs have?
- Studs usually sit at c/c 600 mm, and 560 mm boards then wedge in by friction with no fixings. At a tighter c/c, cut the boards narrower so they fit just as snugly.
- Does it cost anything?
- No, the calculator is free and requires no account.