Insulation calculator

Enter the area and thickness, pick the material — get the coverage with cutting waste, the achieved R-value, the packs to buy and the vapor barrier.

isometricnot to scale

Units

Area length

Area width

Insulation thickness (mm)

Material

Coverage per pack (m²)

Cutting waste %

Include vapor barrier (warm side)

Price per pack (optional)

Estimates are for planning. R-values are nominal for the material — check the actual label of your product.

Material scheduleSheet 01Insulation calculator

Enter the dimensions and press Calculate — the quantities appear here as a printable sheet.

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Frequently asked questions

What R-value do I need for walls and attic?

US guidance for most climate zones: R-13 to R-21 in 2×4/2×6 walls and R-38 to R-49 in the attic. Attic insulation is the cheapest R you can buy — going from R-19 to R-38 up there usually beats any wall upgrade per dollar.

Can I compress insulation batts to fit a thinner cavity?

No — compressing a batt squeezes out the air that does the insulating and cuts its R-value below the label. Use a product made for the cavity depth, or a board insulation with a higher R per inch like XPS.

Which side does the vapor barrier go on?

On the warm-in-winter side: inside the insulation in cold climates, taped at every overlap and penetration. On the cold side use a breathable membrane, never a second vapor barrier — moisture trapped between two barriers rots the assembly.

How much extra insulation should I buy for cuts?

Add about 5% for straight stud bays and 10% when framing is irregular or you are cutting around pipes and boxes. Batts should be cut slightly oversize — about 1/4 in wider than the bay — for a friction fit without gaps.