Insulation Calculator: How Much Insulation Do I Need?
Attic, wall and floor estimates in rolls, batts or bags, matched to your climate zone
How much to buy
Formula: 750 sq ft at R-60, divided by the coverage per bag, plus 10% waste.
Turn these numbers into a build plan.
- 750 sq ft area
- R-60 target
- 25 bags
Cut list: Insulation Calculator: How Much Insulation Do I Need?
- Area750 sq ft
- Target R-valueR-60
- Depth to add24.0 in
- Blown fiberglass25 bags
- DIY material cost$1,050
- Pro installed$750 to $1,650
- BlowerHome centers usually lend the blower free with 10 or more bags.
- [ ] Blown fiberglass25 bags
- [ ] Rafter vent baffles
- [ ] Fire-block spray foam
- [ ] High-temp fire-rated caulk
- [ ] Metal flashing or mineral wool for flue dams
- [ ] Insulation depth rulers
- [ ] IC-rated recessed light covers
Seal air leaks first; the air sealing guide shows where. See what the upgrade saves with the energy savings calculator. Topping up the attic? Next, size your vents with the attic ventilation calculator and keep baffles at every soffit.
Next you will need
Show your build
Finished the insulation calculator: how much insulation do i need?? Snap a before and after. The photo maker lines them up into one image you can post, and a free Blueprint account keeps the photos with your measurements and materials.
Insulate 750 sq ft to R-60
Air seal and insulate a 750 sq ft attic floor to R-60, about 24" more. Plans for 25 bags, baffles at the eaves, and clearance around lights and flues.
- Materials
- $1,199
- Time
- 1 weekend
- Level
- Easy
- 1
Inspect and plan the attic
Measure the 750 sq ft floor, check joist spacing, and find every recessed light, flue, chimney, bath fan and junction box. Fix any roof leaks or moisture first, and get knob-and-tube wiring or vermiculite checked by a pro before touching it.
- Confirm joist spacing (16" or 24")
- Mark lights, flues and junction boxes
- Look for leaks, mold and vermiculite
- 2
Gear up and lay walk boards
Put on the respirator, glasses, gloves and coverall before going up. Lay plywood across the joists as a working platform so you never step on the drywall below.
- Respirator and eye protection on
- Walk boards across joists
- Work light placed
- 3
Air seal before insulating
Foam the top-plate gaps and every wire and pipe penetration, using 2 cans of fire-block foam. Use fire-rated caulk and metal flashing, never foam, against flues and chimneys.
- Seal top plates and penetrations
- Weatherstrip the attic hatch
- Flash and caulk around flues
- Area
- 750 sq ft
- Target
- R-60
- Bags
- 25
- Est. cost
- $1,199
8 steps · 9 tools · 7 materials
5 more steps, the full tool list and a shopping list you can check off as you go.
Your plan is 60% built. Save it.
3/5Insulate 750 sq ft to R-60
Finished in 1 weekend · $1,199 DIY
Built for your area of 750 sq ft. Your first plan saves free. No card needed.
Or save it with just your email
We send a link; open it and this plan is your first project. Your first plan saves free. No card needed.
How to calculate how much insulation you need
R to add = target R - existing depth x R per inch. Depth = R to add / R per inch of the new material. Bags = area / coverage per bag at that R, and batt packages = area / sq ft per package.
- Measure the area. Attic or floor: length x width. Walls: length x height, less about 15 sq ft per window and 20 per door.
- Find your target R-value. Use your climate zone: R-30 to R-60 for attics, R-13 to R-21 in the wall cavity, R-13 to R-38 for floors.
- Subtract what is there. Existing depth x R per inch (about 3.1 for fiberglass batts, 2.5 loose fiberglass, 3.5 cellulose) is the R you already have.
- Convert to depth and units. Depth = R to add / R per inch of the new material. Bags = area / the bag's coverage at that R; packages = area / sq ft per package.
- Add 10% and price it. Add about 10% for waste and fitting, then multiply by the price per bag or package.
Example 1, a 20 x 20 attic in zone 5: the target is R-60 and 3 in of old fiberglass batts gives about R-9, so add R-51: 14.5 in of cellulose, 28 bags with 10% extra, about $448.
Example 2, 40 ft of 8 ft wall with 2 windows, 2x4 at 16 in: 290 sq ft net takes 8 packages of R-13 with 10% extra, about $175.
How many rolls or bags for common attic sizes
| Area | R-value | Blown fiberglass | Cellulose | Fiberglass batts |
|---|---|---|---|---|
| 500 sq ft | R-30 | 8 bags | 18 bags | 17 x R-30 |
| 500 sq ft | R-38 | 10 bags | 23 bags | 16 x R-38 |
| 500 sq ft | R-49 | 12 bags | 30 bags | 18 x R-49 |
| 500 sq ft | R-60 | 15 bags | 36 bags | 17 x R-30 + 9 x R-30 |
| 1,000 sq ft | R-30 | 15 bags | 36 bags | 33 x R-30 |
| 1,000 sq ft | R-38 | 19 bags | 46 bags | 32 x R-38 |
| 1,000 sq ft | R-49 | 24 bags | 59 bags | 35 x R-49 |
| 1,000 sq ft | R-60 | 29 bags | 72 bags | 33 x R-30 + 18 x R-30 |
| 1,500 sq ft | R-30 | 22 bags | 54 bags | 49 x R-30 |
| 1,500 sq ft | R-38 | 28 bags | 69 bags | 47 x R-38 |
| 1,500 sq ft | R-49 | 36 bags | 88 bags | 52 x R-49 |
| 1,500 sq ft | R-60 | 44 bags | 108 bags | 49 x R-30 + 26 x R-30 |
| 2,000 sq ft | R-30 | 29 bags | 72 bags | 65 x R-30 |
| 2,000 sq ft | R-38 | 37 bags | 91 bags | 63 x R-38 |
| 2,000 sq ft | R-49 | 47 bags | 118 bags | 69 x R-49 |
| 2,000 sq ft | R-60 | 58 bags | 144 bags | 65 x R-30 + 35 x R-30 |
Wall insulation R-value by stud size
| Wall | Fiberglass batt | Mineral wool | Dense-pack cellulose |
|---|---|---|---|
| 2x4 (3.5 in) | R-13 or R-15 | R-15 | about R-13 |
| 2x6 (5.5 in) | R-19 or R-21 | R-23 | about R-20 |
Zones 5 and up call for continuous foam outside the studs as well (R-5 to R-10). Batt sizes and coverage:
| Batt | Thickness | Sq ft per package (16 in) | Sq ft per package (24 in) |
|---|---|---|---|
| R-13 fiberglass | 3.5 in | 40 | 106 |
| R-15 fiberglass | 3.5 in | 30 | 45 |
| R-19 fiberglass | 6.25 in | 49 | 75 |
| R-21 fiberglass | 5.5 in | 40 | 60 |
| R-30 fiberglass | 10 in | 31 | 58 |
| R-38 fiberglass | 12 in | 32 | 53 |
| R-49 fiberglass | 16 in | 29 | 43 |
| R-15 mineral wool | 3.5 in | 60 | 90 |
| R-23 mineral wool | 5.5 in | 30 | 45 |
| R-30 mineral wool | 7.25 in | 25 | 38 |
What R-value is the insulation I already have?
| Type | R per inch | 4 in | 6 in | 10 in |
|---|---|---|---|---|
| Fiberglass batts | 3.1 | R-12 | R-19 | R-31 |
| Loose fiberglass | 2.5 | R-10 | R-15 | R-25 |
| Cellulose | 3.5 | R-14 | R-21 | R-35 |
| Rock wool | 3 | R-12 | R-18 | R-30 |
| Vermiculite (test for asbestos, do not disturb) | 2.2 | R-9 | R-13 | R-22 |
Safety, rebates and air sealing
- Vermiculite can contain asbestos. Have it tested and do not disturb it.
- Knob-and-tube wiring must not be buried in insulation; get an electrician to check or replace it first.
- Keep insulation 3 in from flues, chimneys and recessed lights that are not IC-rated.
- Keep soffit vents open with a baffle in every rafter bay at the eaves.
The federal 25C energy efficiency credit ended for work placed in service after 2025, but many utilities and states still pay rebates for attic insulation and air sealing; check yours before you buy. Seal leaks first with the air sealing guide and the home energy audit checklist, and see the insulation R-value cheat sheet for basements and rim joists.
What R-value do I need in my attic?
Most of the US should insulate an attic floor to R49 to R60; only the warmest zone stops at R30. Seal air leaks around lights, pipes and the hatch first: insulation slows heat, but it does not stop air.
| Zone | Where | Attic | Fiberglass batts | Blown fiberglass | Blown cellulose |
|---|---|---|---|---|---|
| 1 | South Florida, Hawaii | R30 to R49 | 9.7 in | 12.0 in | 8.6 in |
| 2 | Gulf Coast, south Texas | R49 to R60 | 15.8 in | 19.6 in | 14.0 in |
| 3 | Southeast, southern California | R49 to R60 | 15.8 in | 19.6 in | 14.0 in |
| 4 | Mid-Atlantic, Kansas, Pacific Northwest | R60 | 19.4 in | 24.0 in | 17.1 in |
| 5 to 8 | Northeast, Midwest, mountain states, Alaska | R60 | 19.4 in | 24.0 in | 17.1 in |
R-value per inch by material
- Fiberglass batts: about R-3.1 per inch
- Blown fiberglass: about R-2.5 per inch
- Blown cellulose: about R-3.5 per inch
- Closed-cell spray foam: about R-6.5 per inch
Values are typical; the bag or batt label is what counts. Check a whole wall assembly with the wall R-value calculator, estimate payback with the energy savings calculator, and see the insulation R-value cheat sheet for walls, floors and basements.
Insulation calculator FAQ
How many rolls of insulation do I need?
How many bags of blown-in insulation for 1,000 sq ft?
Batts or blown-in for walls?
Can I blow insulation into existing walls?
Is the Home Depot or Lowe's insulation calculator the same?
What R-value for a crawl space or floor?
How do I measure my attic?
What R-value do I need in my attic?
Can I add insulation over old insulation?
Related calculators
All calculatorsRelated cheat sheets
All cheat sheetsHome Energy Savings Audit
Complete guide to identifying energy waste and reducing power bills through efficiency improvements
Insulation R-Value Guide
R-value requirements by climate zone for attics/walls/floors, fiberglass batts vs blown-in cellulose vs spray foam (open/closed cell) vs rigid foam, coverage calculations, vapor barrier placement
Weatherstripping & Air Sealing Guide
Weatherstrip types by application, door sweeps, foam sealants, and priority sealing locations