Insulation calculator
Cavity area to insulate, by assembly. Depth and R-value drive the price more than the area does.
Insulation
Cavity area to insulate, by assembly. Depth and R-value drive the price more than the area does.
Batts come 15 or 23 in wide to suit stud spacing. Blown depth is what gets you the R-value.
$956
1,470 sq ft of fibreglass batt r-13 at $0.65 / sq ft
Free. No signup. The quantities carry over as line items.
How this insulation calculator works
Cavity area by assembly. The area is the easy half — the depth and R-value you choose drive both the price and whether the job actually performs.
The formula
area to order = cavity area × (1 + waste)
Assumptions and defaults
| Default waste | 5% |
| Batt bag coverage | about 40 sq ft |
| 2×4 wall | R-13 to R-15 |
| 2×6 wall | R-19 to R-21 |
Pro tips
Batts only hit their rating if they fill the cavity without compression. A compressed R-21 in a 2×4 bay performs worse than a properly fitted R-13.
Air sealing before insulating buys more comfort per dollar than the next R-value up. Foam the top plates and penetrations first.
In an attic, measure depth not area for blown product — the coverage chart on the bag is by depth at a target R.
Common questions
How much insulation do I need?
Enter the cavity area you are filling and pick the assembly. The calculator adds five per cent for offcuts around blocking and wiring.
What R-value should I use?
R-13 to R-15 in 2×4 walls, R-19 to R-21 in 2×6, and R-38 to R-60 in attics depending on climate zone. Check your local code before you order.
Batts or blown insulation?
Batts in open walls, blown in attics. Blown fills around obstructions better and goes faster over a big flat area.
Is spray foam worth the price?
Where you need air sealing and R-value in one pass and the cavity is shallow, yes. In a normal 2×6 wall with good detailing, batts and a careful air seal get close for much less.