1,200 sq ft · 10% · 40 sq ft bag
Input
Attic floorOutput
33 bags1,320 ÷ 40 = 33 bags.
Insulation quantity is **net area × (1 + waste%)**, rounded up to whole batt bags using **sq ft per package** from the manufacturer label.
**Formula:**
Sq ft to order = Net area sq ft × (1 + waste% / 100)
Bags = ceil(Sq ft to order ÷ Sq ft per bag)
**Example — 1,200 sq ft attic, 10% waste, 40 sq ft/bag:**
1,320 sq ft → **33 bags**
Net insulated area times waste buffer, divided by package coverage for bag count.
Formula
sq_ft_order = net_sq_ft × (1 + waste%); bags = ceil(sq_ft_order / bag_sq_ft)Tap 1,200 sq ft attic, 400 sq ft walls, or enter insulated sq ft on the main form.
R-13, R-19, or R-30 presets set bag size and waste on the main form.
Read from the batt label — often 40–58 sq ft depending on R-value.
Enable door and window deductions for wall cavity mode.
Results show insulation to order, bag count, and purchase guide.
Input
Attic floorOutput
33 bags1,320 ÷ 40 = 33 bags.
Input
Wall cavityOutput
9 bags440 ÷ 49 = 8.98 → 9 bags.
Input
Crawl spaceOutput
22 bags880 ÷ 40 = 22 bags.
Input
12×12 room wallsOutput
4 bags158.4 ÷ 40 = 3.96 → 4 bags.
Common real-world scenarios where this tool saves time.
1,320 sq ft with 10% waste, 40 sq ft bags = 33 bags.
Deduct 2 doors and 4 windows before bag count.
Floor joist bays — 10% waste, R-19 batts.
Step-by-step chains that connect related tools for common tasks.
| R-value | Sq ft / bag |
|---|---|
| R-13 (2×4 wall) | 40 |
| R-19 (2×6 wall) | 49 |
| R-30 (attic) | 58 |
| Sq ft / bag | Bags needed |
|---|---|
| 40 sq ft | 33 bags |
| 49 sq ft | 27 bags |
| 58 sq ft | 23 bags |
Match R-value to cavity depth — R-13 for 2×4, R-19 for 2×6.
Cuts around pipes and corners always waste material — **10% minimum**.
Attic uses **floor** sq ft; walls use perimeter × height minus openings.
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1,200 sq ft with 10% waste (1,320 sq ft) and 40 sq ft bags: 33 bags.
10% for batts in open bays; 15% for blown-in or complex framing.
Manufacturer coverage per package at stated R-value — often 40–58 sq ft on the label.
R-13 fits 2×4 walls; R-19 fits 2×6 walls or floors. Check local energy code.
Enable door and window deductions for exterior wall cavity estimates — attic floor mode uses gross floor area without openings.
Insulate cavities before drywall — use Drywall Calculator for sheet count after.
Enter bag coverage from blown-in packaging; use 15% waste preset for attic blow.
Length × width of insulated floor, or enter total sq ft in area mode.
Switch to metric — enter m² and sq ft per bag from the label.
Partial batts are not sold — always round up to whole packages.
Area dimensions stay on your device — no upload to EverydayTools servers.
Estimates only — verify R-value requirements with local building code and manufacturer install guide.
Part of Calculator Tools
More free tools for the same workflow.
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Reviewed on 2026-06-27.
2×4 wall cavity
Read from the batt label — often 40–58 sq ft depending on R-value and thickness.