CalcLibrary

Insulation Calculator

Estimate how many insulation packs, rolls, or boards to buy for a wall, attic, floor, or ceiling job. Enter area directly or use a quick length x width helper, subtract openings, add waste, and see the rounded-up purchase count plus leftover coverage.

Units
m²
m²
m²
%
Examples

Direct entry for a 48 m² wall area, 9.5 m² of windows and doors, 5.6 m² per pack, and 10% waste.

Packs to buy
8
Gross area
48 m²
Net area after openings
38.5 m²
Adjusted area with waste
42.35 m²
Coverage purchased
44.8 m²
Leftover coverage
2.45 m²

Whole packages only. The rows below show the extra coverage created by rounding up.

Buying estimate only. This tool uses your area, opening deductions, waste percentage, and package coverage. It does not determine code, R-value/U-value, or the best insulation product.

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Examples

How It Works

Formula

Ag={Addirect area entryL⋅Wlength x width helperA_g = \begin{cases} A_d & \text{direct area entry} \\ L \cdot W & \text{length x width helper} \end{cases}

An=Ag−AoA_n = A_g - A_o

Aa=An⋅(1+w100)A_a = A_n \cdot \left(1 + \frac{w}{100}\right)

N=⌈AaAp⌉N = \left\lceil \frac{A_a}{A_p} \right\rceil

Ab=N⋅ApA_b = N \cdot A_p

Al=Ab−AaA_l = A_b - A_a

Variables

AdA_d

Direct area entry(m²)

LL

Length of the rectangular section(m)

WW

Width of the rectangular section(m)

AgA_g

Gross area before openings(m²)

AoA_o

Opening area to subtract(m²)

AnA_n

Net area after openings(m²)

ww

Waste allowance(%)

AaA_a

Adjusted area after waste(m²)

ApA_p

Coverage of one package(m²)

NN

Packages to buy (rounded up)

AbA_b

Coverage purchased after rounding(m²)

AlA_l

Leftover coverage after rounding(m²)

Choose the surface you are planning for, then enter the job size either as a direct area or as length x width for a simple rectangle. The calculator subtracts any opening area you enter, multiplies the remaining area by your waste percentage, divides by the coverage of one package, and rounds up to whole packages. The supporting rows stay visible so you can see exactly how waste or package coverage changed the buy quantity.

Frequently Asked Questions

01What should I enter for coverage per package?
Use the coverage printed for the exact product you plan to buy. If the label says one pack covers 5.6 m² or 60 ft², enter that number and match the unit system at the top of the page.
02Should I subtract openings?
Subtract openings when they will stay uninsulated and you want a tighter purchase estimate. If you prefer a rougher buy, leave openings at 0 and rely on the waste percentage you choose.
03Why is there leftover coverage?
Because the calculator rounds up to whole packages after applying waste. The leftover row shows how much extra coverage that round-up creates.
04Does this calculator choose insulation type or code requirement?
No. It only does coverage math from your inputs. It does not determine required R-values or U-values, local code, rebates, climate guidance, or the best insulation product.

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