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Insulation roll chart
Put your area and roll coverage in: 400 sq ft at 10% waste with 40 sq ft rolls needs 11.00 rolls exact, order 11.
★ CONSTRUCTION · INSULATION · ROLL CHART
Insulation Roll Chart: 11 Rolls for a 400 Sq Ft Area
On the defaults — a 400 sq ft area at 10% waste with 40 sq ft insulation rolls — you need 11.00 rolls exact: order 11 rolls. This is the ROLL version — rolls counted by coverage — the plywood-sheet-chart page is the SHEET version — the same waste-and-round-up model on sheet goods; the drywall-coverage-chart page is the DRYWALL version — sheets by area and size; and the insulation-coverage-chart page is the BAG version — loose-fill bags by area and R-value, not rolls.
What does 11.00 rolls, order 11, mean?
It means that a 400 sq ft area, once a 10% waste allowance is added, needs 440 sq ft of insulation, and at 40 sq ft a roll that is exactly 11.00 rolls — so you order 11 rolls and no extra roll is added for rounding, because the fit is already exact. The waste allowance is the whole story in miniature: without it the same area would need exactly 10.00 rolls, so the allowance is worth one whole roll here, and a careless order of 10 rolls would leave 40 sq ft — a tenth of the job — uncovered. The part people get wrong is rounding the exact figure twice: 11.00 already includes the waste, so ordering 12 “just in case” adds a second, hidden allowance of another 9%, and on a bigger job that habit quietly buys a roll too many on every order.
Three things to check before you trust the number
Is 40 sq ft really your roll’s coverage? Roll coverage is width times length, and the common 15-inch by 32-foot roll is 1.25 feet times 32 feet, which is exactly 40 sq ft — but rolls also come in 24-inch widths and shorter lengths. The 32 sq ft branch needs 13.75 rolls, order 14, and the 64 sq ft branch needs 6.88, order 7, so a wrong coverage figure moves the order by whole rolls. Read the label, multiply width by length, and use that figure.
Is 10% waste enough for your layout? Ten percent covers straight runs with ordinary cutting, but bays full of obstacles — wiring, pipes, recessed lights, odd angles — can push real waste to 15% or 20%, and every extra 10% on 400 sq ft is another 40 sq ft, or one more roll. The 800 sq ft branch orders 22 rolls, so on a large area a waste error compounds fast. If your layout is cut up, price the job at 15% waste first and compare.
Are you insulating one layer or two? This page counts one layer at the roll coverage you enter. Doubling up for a higher R-value doubles the rolls: two layers over 400 sq ft need 22 rolls, not 11, and the lookup table below is per layer. If your target R-value needs two layers, run the page once per layer or double the order — do not let a single-layer figure order half a job.
Worked example
On the defaults: 400 sq ft area, 40 sq ft roll coverage, 10% waste allowance.
- Needed area: 400 × 1.10 is 440 sq ft.
- Exact rolls: 440 ÷ 40 is 11.00 rolls.
- Order: 11.00 rounded up is 11 rolls — an exact fit, so no extra roll is added.
And the other way: the area needing exactly 11.00 rolls at 40 sq ft a roll is 400 sq ft, the roll coverage needing exactly 11.00 rolls over 400 sq ft is 40 sq ft, and the area needing exactly 22.00 rolls at 40 sq ft a roll is 800 sq ft.
Every branch, checked
- 200 sq ft area, 40 sq ft rolls: 200 sq ft area, 40 sq ft rolls: 5.50 rolls exact — order 6 rolls.
- 800 sq ft area, 40 sq ft rolls: 800 sq ft area, 40 sq ft rolls: 22.00 rolls exact — order 22 rolls.
- 400 sq ft area, 32 sq ft rolls: 400 sq ft area, 32 sq ft rolls: 13.75 rolls exact — order 14 rolls.
- 400 sq ft area, 64 sq ft rolls: 400 sq ft area, 64 sq ft rolls: 6.88 rolls exact — order 7 rolls.
- 100 sq ft area, 40 sq ft rolls: 100 sq ft area, 40 sq ft rolls: 2.75 rolls exact — order 3 rolls.
- 1,000 sq ft area, 40 sq ft rolls: 1,000 sq ft area, 40 sq ft rolls: 27.50 rolls exact — order 28 rolls.
The reverses, worked backwards
- Area needing exactly 11.00 rolls at 40 sq ft a roll: 400 sq ft — at 400 sq ft the figures are 11.00 rolls exact — order 11 rolls.; at the lower neighbor the figures are 9.63 rolls exact — order 10 rolls.; at the upper neighbor the figures are 12.38 rolls exact — order 13 rolls..
- Roll coverage needing exactly 11.00 rolls over 400 sq ft: 40 sq ft — at 40 sq ft the figures are 11.00 rolls exact — order 11 rolls.; at the lower neighbor the figures are 12.22 rolls exact — order 13 rolls.; at the upper neighbor the figures are 10.00 rolls exact — order 10 rolls..
- Area needing exactly 22.00 rolls at 40 sq ft a roll: 800 sq ft — at 800 sq ft the figures are 22.00 rolls exact — order 22 rolls.; at the lower neighbor the figures are 20.63 rolls exact — order 21 rolls.; at the upper neighbor the figures are 23.38 rolls exact — order 24 rolls..
What the defaults assume
The defaults are a 400 sq ft area, 40 sq ft rolls and a 10% waste allowance, so the headline is a single room or attic section insulated in one layer of standard rolls. The model is a multiplication, a division and a ceiling: needed area is area times 1.10, exact rolls are needed area divided by roll coverage, and the order rounds exact rolls up to the next whole roll, with a 1e-9 epsilon so an exact whole number orders exactly that many. The area reverse is checked at 50 sq ft either side, because 50 sq ft times 1.10 over 40 sq ft is 1.375 rolls; the roll reverse is checked at 4 sq ft either side, because 440 over 36 is 12.22 rolls and over 44 is exactly 10.00. The model does not include compression, offcut reuse, double layers, or vapor-barrier and fastener quantities — count those separately.
Lookup table: rolls by area and roll size
Each row already includes the 10% waste allowance: needed area is the area times 1.10, exact rolls are needed area divided by roll coverage, and the order column rounds up. A row that lands exactly on a whole number orders exactly that many — no extra roll is added for an exact fit.
| Area | Roll coverage | Needed area | Exact rolls | Order |
|---|---|---|---|---|
| 100 sq ft | 32 sq ft | 110 sq ft | 3.44 | 4 rolls |
| 100 sq ft | 40 sq ft | 110 sq ft | 2.75 | 3 rolls |
| 200 sq ft | 32 sq ft | 220 sq ft | 6.88 | 7 rolls |
| 200 sq ft | 40 sq ft | 220 sq ft | 5.50 | 6 rolls |
| 300 sq ft | 32 sq ft | 330 sq ft | 10.31 | 11 rolls |
| 300 sq ft | 40 sq ft | 330 sq ft | 8.25 | 9 rolls |
| 400 sq ft | 32 sq ft | 440 sq ft | 13.75 | 14 rolls |
| 400 sq ft | 40 sq ft | 440 sq ft | 11.00 | 11 rolls |
| 500 sq ft | 32 sq ft | 550 sq ft | 17.19 | 18 rolls |
| 500 sq ft | 40 sq ft | 550 sq ft | 13.75 | 14 rolls |
| 600 sq ft | 32 sq ft | 660 sq ft | 20.63 | 21 rolls |
| 600 sq ft | 40 sq ft | 660 sq ft | 16.50 | 17 rolls |
| 800 sq ft | 32 sq ft | 880 sq ft | 27.50 | 28 rolls |
| 800 sq ft | 40 sq ft | 880 sq ft | 22.00 | 22 rolls |
| 1,000 sq ft | 32 sq ft | 1,100 sq ft | 34.38 | 35 rolls |
| 1,000 sq ft | 40 sq ft | 1,100 sq ft | 27.50 | 28 rolls |
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Needed area | area × 1.10 | 440 sq ft — 400 × 1.10. |
| Exact rolls | needed area ÷ roll coverage | 11.00 rolls — 440 ÷ 40. |
| Order | exact rolls rounded up | 11 rolls — 11.00 is already whole. |
| Area needing exactly 11.00 rolls | exact rolls × roll coverage ÷ 1.10 | 400 sq ft — 11.00 × 40 ÷ 1.10. |
| Roll coverage needing exactly 11.00 rolls | needed area ÷ exact rolls | 40 sq ft — 440 ÷ 11.00. |
| Area needing exactly 22.00 rolls | exact rolls × roll coverage ÷ 1.10 | 800 sq ft — 22.00 × 40 ÷ 1.10. |
| 200 sq ft area, 40 sq ft rolls | same model | 5.50 rolls exact — order 6 rolls. |
| 800 sq ft area, 40 sq ft rolls | same model | 22.00 rolls exact — order 22 rolls. |
| 400 sq ft area, 32 sq ft rolls | same model | 13.75 rolls exact — order 14 rolls. |
| 400 sq ft area, 64 sq ft rolls | same model | 6.88 rolls exact — order 7 rolls. |
| 100 sq ft area, 40 sq ft rolls | same model | 2.75 rolls exact — order 3 rolls. |
| 1,000 sq ft area, 40 sq ft rolls | same model | 27.50 rolls exact — order 28 rolls. |
| Area needing exactly 11.00 rolls at 40 sq ft a roll | reverse | 400 sq ft: 11.00 rolls exact — order 11 rolls. |
| Roll coverage needing exactly 11.00 rolls over 400 sq ft | reverse | 40 sq ft: 11.00 rolls exact — order 11 rolls. |
| Area needing exactly 22.00 rolls at 40 sq ft a roll | reverse | 800 sq ft: 22.00 rolls exact — order 22 rolls. |
| 0 sq ft area | same model | 0.00 rolls exact — order 0 rolls. |
| Negative area | same model | Area — 0 or more. |
| Negative roll coverage | same model | Roll coverage — more than 0. |
| 400 sq ft area, 44 sq ft rolls | same model | 10.00 rolls exact — order 10 rolls. |
Who uses this
- A DIYer insulating an attic or wall — 400 sq ft at 10% waste with 40 sq ft rolls is 11 rolls, with the lookup table covering every other room size without re-measuring.
- A contractor ordering for a job — the branches show how the order moves with area and roll size, so a supplier substitution from 40 to 32 sq ft rolls is repriced before ordering.
- A homeowner comparing roll sizes — the 32 and 64 sq ft branches show whether the bigger roll actually saves rolls or just changes the rounding.
- An energy auditor estimating material — the reverses recover the area or roll size behind any quoted roll count, which checks a quote without re-measuring the job.
Accuracy & limitations
Figures are the model’s own arithmetic on the numbers you type, computed from unrounded values and displayed rounded HALF_UP to 2dp, with orders rounded up using a 1e-9 epsilon so exact fits are not over-ordered. The main limitation is the waste allowance, not the arithmetic: cut-up layouts waste more than 10%, and roll coverage varies by product, so check the label. This page is a calculation tool, not building advice — follow local code for R-values, vapor barriers and fire safety.
Cite this calculator
A 400 sq ft area at 10% waste with 40 sq ft insulation rolls needs 11.00 rolls exact: order 11 rolls. Source: Bright Side Kit, https://brightoolbox.com/insulation-roll-chart/, accessed 29 October 2026.
Frequently asked questions
How do I find a roll’s coverage?
Multiply its width by its length in feet: a 15-inch (1.25-foot) by 32-foot roll covers 40 sq ft. The figure is usually printed on the label too — if the label and your multiplication disagree, trust the label and check whether the roll is sold by covered area or by roll length.
Why 10% waste?
Ten percent is the standard allowance for cutting, fitting around obstacles and end-of-roll offcuts on straightforward runs. Straight, unobstructed bays waste less; bays full of wiring, pipes and odd angles waste more — price cut-up layouts at 15% or higher.
What if the exact figure is already a whole number?
Then you order exactly that many: 11.00 rolls orders 11, not 12. The waste allowance is already inside the exact figure, so adding another roll for luck double-counts the allowance.
What is the difference between rolls, batts and bags?
Rolls are continuous lengths cut on site; batts are pre-cut pieces for standard stud spacing; bags are loose-fill blown in by machine. This page counts rolls only — the bag version is the insulation-coverage-chart page, which prices by R-value.
Do I double the order for two layers?
Yes: this page counts one layer. Two layers over the same area need twice the rolls, so a 400 sq ft area at two layers orders 22 rolls, and the lookup table below is per layer.
What about cutting waste around joists and obstacles?
That waste is what the 10% allowance is for, but it is an average, not a guarantee. On a joist layout with many short offcuts, measure one bay, count its offcuts, and scale the waste percentage to what you actually see before ordering for the whole job.