Insulation Calculator
Calculate insulation needed
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Insulation Calculator helps you calculate insulation needed — free, instant, in your browser. Type Area (m²), Desired R-Value and Material Thickness (m) into Insulation; each keystroke re-runs the math. In Insulation the working sits beside the answer. Use Insulation for a reliable number, fast. You can disconnect once Insulation has loaded; the arithmetic runs locally. Insulation is part of the Construction collection on CalcProMaster, alongside free insulation calculator, free online insulation calculator and more. Run Insulation twice to find the driving input. Insulation stays bookmarked for next time.
What the defaults give
100 m² of area needs 10 rolls at the tool's ten-square-metre roll coverage.
The material check: 0.1 m of thickness for an R-5 target gives a k-value of 0.02 W/m·K, which is a realistic mineral-wool figure.
How much insulation you need
The quantity follows straight from the area and the thickness that delivers your target R-value:
Volume = Area × Thickness, and R-value = Thickness ÷ Conductivity
For 100 m² at 0.1 m thickness: 100 × 0.1 = 10 m³ of insulation.
| Area (m²) | Thickness (m) | Volume (m³) |
|---|---|---|
| 50 | 0.1 | 5.0 |
| 100 | 0.1 | 10.0 |
| 100 | 0.2 | 20.0 |
| 150 | 0.15 | 22.5 |
| 200 | 0.2 | 40.0 |
Thicker insulation raises the R-value but multiplies the volume, so check the target R-value for your climate first. Related: drywall and construction calculators.
The two calculations
Rolls = ceil(area ÷ 10) → 100 ÷ 10 = 10 rolls.
k-value = thickness ÷ R-value → 0.1 ÷ 5 = 0.02 W/m·K.
Worked examples
100 m² at R-5 → 10 rolls, k 0.02
150 m² at R-5 → 15 rolls
100 m² at R-7 with 0.1 m → k 0.0143 (a better insulator)
100 m² at R-3 with 0.1 m → k 0.0333 (a poorer one)
Why the k-value matters
R-value tells you how much the assembly resists heat flow; the k-value (thermal conductivity) tells you how good the material is per metre. The same R-value can be reached with a poor insulator only by making it thicker, which is why a wall cavity has a finite depth and a target R-value implies a minimum material thickness. Lower k is better.
Where the estimate is approximate
- Roll coverage is fixed at 10 m². Real rolls vary from about 5 to 12 m² depending on thickness and manufacturer, so check the pack before buying.
- It is area only. Joists, studs and noggins break the run into bays that each need cutting.
- Thermal bridging is ignored. Wood studs conduct far better than insulation, so a framed wall performs below its nominal R-value.
- Air sealing comes first. An insulated draughty wall loses more heat than its R-value suggests; sealing gaps is usually the cheaper first step.
Add 5–10% for offcuts on a framed wall, and check the local code for the minimum R-value in your climate zone before choosing a thickness.
The k-value here is derived from the requested R-value and the material thickness, which reverses the usual shopping order. What matters on site is that R-value is additive: two layers of R-5 give R-10, while compressing a batt lowers its R-value rather than raising it. Gaps and thermal bridging around studs and joists cut installed performance well below the label, so the roll count is a material estimate, not a guarantee of the R-value the wall will achieve.
Frequently Asked Questions
How many rolls do I need for 100 m²?
Ten, at the tool's ten-square-metre roll coverage. Check the actual coverage printed on the roll, because packs range from about 5 to 12 m².
What does a k-value of 0.02 mean?
That the material conducts 0.02 watts per metre per kelvin, which is typical of mineral wool. Lower numbers are better insulators.
How is thickness related to R-value?
R = thickness divided by conductivity, so doubling the thickness doubles the R-value for the same material.
Does the calculator include waste?
No. Add 5–10% for cuts and offcuts, and more if the wall has many openings or irregular bays.
What is thermal bridging?
Heat flowing through timber studs or metal fixings that bypass the insulation. It can cut a wall's effective performance by 10–20%.
Should I insulate or draught-proof first?
Draught-proofing first. Sealing gaps is cheap and prevents the air movement that makes insulation work harder than its R-value implies.
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