Calculating your batts/rolls needed is straightforward once you know the Insulation formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Insulation Calculator.
What is Insulation?
The Insulation calculation tells you your batts/rolls needed from a few simple inputs. The figure you are solving for here is the batts/rolls needed.
The Insulation formula
This calculation combines several inputs through a multi-step method rather than a single one-line formula. Enter the values below and the calculator resolves each step in order. The inputs it needs are:
- Area length — a value measured in m. Example: 10 m.
- Area width — a value measured in m. Example: 5 m.
- Area per batt/roll — a value measured in m². Example: 0.7 m².
- Wastage allowance — a percentage, such as an annual rate. Example: 5%.
How to calculate it step by step
- Write down the area length (for example, 10 m).
- Write down the area width (for example, 5 m).
- Write down the area per batt/roll (for example, 0.7 m²).
- Write down the wastage allowance (for example, 5%).
- Apply the formula above to get your batts/rolls needed.
- Double-check the result with the Insulation Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Area length | 10 m |
| Area width | 5 m |
| Area per batt/roll | 0.7 m² |
| Wastage allowance | 5% |
| Batts/rolls needed | 75 |
| Area to insulate | 50.00 |
With area length of 10 m, area width of 5 m, area per batt/roll of 0.7 m² and wastage allowance of 5%, the batts/rolls needed works out to 75.
Example 2
With area length of 20 m, area width of 5 m, area per batt/roll of 0.7 m² and wastage allowance of 5%, the batts/rolls needed works out to 150.
| Result | Value |
|---|---|
| Batts/rolls needed | 150 |
| Area to insulate | 100.00 |
Example 3
With area length of 5 m, area width of 5 m, area per batt/roll of 0.7 m² and wastage allowance of 5%, the batts/rolls needed works out to 38.
| Result | Value |
|---|---|
| Batts/rolls needed | 38 |
| Area to insulate | 25.00 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Insulation Calculator does it instantly, for free, with the formula and a worked example built in.
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