Before you start, you’ll want: a tape measure, and a rough idea of which space you’re insulating. That’s it. Everything else the tool works out for you.
How to Use Our Insulation Calculator
Four answers get you an estimate: which space, how big it is, which material, and how much insulation you want. The calculator does the rest in about thirty seconds.
Here’s the whole job in one sentence, because it makes everything else easier to follow:
Every insulation project is the same thing — cover this much space, with this material, to this level of protection.
Those three things are all you’re choosing. The calculator turns them into a shopping list and a price.
1. Choose the space you’re insulating
Start here, because it changes everything after it. Each space needs a different amount of insulation, and some materials only work in some places. Pick one, and the tool hides the options that don’t apply.
Doing more than one space? Run it once for each, and the totals add up as you go.
2. Enter the size of that space
This is the step people get wrong, so take a minute over it. Insulation calculator square feet means the size of the surface you’re covering — not the size of your house.
- Floor, ceiling or attic: measure the length and the width, and multiply them.
- Wall: walk the outside of the house and add up the lengths to get the distance around it. Multiply that by the height of the wall. Then take off the doors and windows, since you’re not insulating those.
A 1,500 sq ft house does not have 1,500 sq ft of attic, and it doesn’t have 1,500 sq ft of wall either. Entering your house size here is the number one reason an estimate comes out wrong.
Measure your own doors and windows if you can — add them up and subtract the total. Where that isn’t practical, roughly a fifth of the wall face is the figure estimators fall back on, and it holds for a house with ordinary window area. A wall of glass needs measuring.
Already got some insulation? Enter roughly how deep it is and what it looks like. The tool subtracts it, so you only price the difference.
3. Pick a material
Six choices. Batts and rolls come in bundles. Loose-fill comes in bags. Rigid board comes in 4 ft × 8 ft sheets.
Every package tells you how much floor or wall it covers. The tool takes your measurement, divides it by that coverage, and rounds up to whole packages — the same way the store sells it. So the number you get is the number you buy, not something you have to work out at the register.
Not sure which material? The next section walks through it.
4. Say how much insulation you want
This is the R-value. Two ways to answer:
- Easiest: choose recommend for my climate, and the tool picks a sensible level based on your state.
- If you already know: type your own number.
5. Tell it DIY or professional
This only changes the price, not the amount. DIY shows you material cost. Professional adds the crew and the prep work — what a quote from us would look like.
6. Read your result
Your four numbers come back together. The quantity is rounded up to whole packages, because that’s how insulation is sold — but nothing extra is added on top of that. Installers normally allow another 5 to 15% for offcuts, compression and mistakes, so buy a little over the number and return what you don’t open. Nobody ever finishes a job with exactly the right amount.
Want to see the math the tool ran? It’s written out further down, in five short steps.
How Much Insulation Do I Need?
A 1,500 sq ft single-story home needs about 1,200 sq ft of attic covered and about 1,300 sq ft of wall — different amounts, and often different materials, for each.
The confusion is nearly always the same. “A 1,500 sq ft house” is the size of the floor you walk on. It is not the area you’re insulating, and the real number is different for every part of the house.
How much insulation for a 1,500 sq ft house?
Picture a single-story home, about 32 ft by 47 ft.
- Attic: about 1,200 sq ft. Nearly the whole footprint. You lose a strip around the edge where the roof comes down and there’s no room to work, and the garage doesn’t count if it sits outside the heated part of the house.
- Walls: about 1,280 sq ft. It’s 158 ft around the outside, times 8 ft high. Take out the doors and windows and you’re actually covering around 1,050 sq ft.
- Floor: the full 1,500 sq ft, if there’s a crawl space or an unheated basement underneath.
One house, three surfaces, three different numbers. That’s why the house insulation calculator here works one space at a time instead of pretending a single figure covers everything.
How much to insulate a 2,000 sq ft house?
The number of floors matters more than the square footage.
A single-story 2,000 sq ft home has roughly 1,600 sq ft of attic.
A two-story one sits on half the ground, so it only has around 800 sq ft of attic. But it has about 2,080 sq ft of outside wall, because you’re wrapping two floors instead of one.
Same size house. Half the attic, nearly double the wall.
| House size | Floors | Attic (sq ft) | Wall (sq ft) | Floor over cold space (sq ft) |
|---|---|---|---|---|
| 1,000 sq ft | 1 | ~800 | ~1,040 | ~1,000 |
| 1,500 sq ft | 1 | ~1,200 | ~1,280 | ~1,500 |
| 2,000 sq ft | 1 | ~1,600 | ~1,460 | ~2,000 |
| 2,000 sq ft | 2 | ~800 | ~2,080 | ~1,000 |
| 2,500 sq ft | 2 | ~1,000 | ~2,300 | ~1,250 |
Based on a simple rectangular house with 8 ft walls, and wall figures before doors and windows come off. Use it to check your own numbers look about right — then measure properly before you order.
How many sq ft per roll of insulation?
A 15-inch-wide roll of R-13 — the standard size for framing set 16 inches apart — covers about 40 sq ft. The wider 23-inch roll, for framing 24 inches apart, covers about 60.
Here’s the catch: the more insulating a roll does, the less ground it covers. Thicker material means less of it fits on the roll. So an R-19 roll doesn’t stretch as far as an R-13 roll of the same length, and an R-30 bundle covers less again.
That’s why you can’t swap between products by eye. Read the coverage figure off the package you’re actually buying, and enter that.
Doing an attic? Loose-fill settles after it’s blown, so the math is a bit different — our attic and blown-in insulation calculator handles that.
Insulation Types Compared: Which Should You Enter?
Batts are the cheapest way to insulate an open wall or ceiling. Loose-fill is the only sensible choice over an attic that already has insulation. Spray foam costs the most and seals air leaks at the same time. Rigid board goes where nothing else will fit.
After the R-value, this is the choice that moves your estimate most. We install all six of these and make none of them, so we’ve no reason to push you toward any one.
In a sentence each:
- Batts — pre-cut pieces that slot between the studs and joists. You need to be able to see the framing.
- Rolls — the same stuff, but in one long piece you cut yourself. Good for long clear runs.
- Loose-fill — blown in loose, so it flows over beams, wires and old insulation instead of having to fit around them.
- Spray foam — sprayed on wet and swells up. Open-cell is lighter and cheaper; closed-cell is denser and does more per inch.
- Rigid board — flat panels you cut and tape, rather than tuck in.
- Mineral wool — a heavier batt, used where fire or noise matters.
Two questions usually settle it: can you see the framing, and is there already insulation there?
| If this is true | Usually the answer | Why |
|---|---|---|
| You can see the framing and can reach it | Batts or rolls | Cheapest way to get there, and quickest to fit |
| There’s already insulation in the attic | Loose-fill | Flows over the old stuff without disturbing it |
| You want to stop drafts as well | Spray foam | The only one that seals and insulates at once |
| There’s no gap to fill | Rigid board | Goes on the face of the wall, or under a slab |
| Fire or noise is the concern | Mineral wool | Heavier, and it doesn’t melt as easily |
| The gap is shallow but you want a lot | Closed-cell spray foam or rigid board | They do the most per inch, so it fits |
One more thing you’ll see on the package. Faced insulation has a paper or foil backing that keeps moisture out. Unfaced doesn’t. If you’re adding on top of insulation that already has a backing, use unfaced — two backings trap damp in between.
Each material has its own way of being counted. For attic loose-fill, that’s our blown-in insulation calculator; for spray foam, which is quoted by the board foot rather than the square foot, our spray foam insulation calculator; and for R-value per inch by product, our R-value chart has the figures.
R-Value Calculator: What Should You Enter?
Let the calculator pick it from your state, or type your own. The Department of Energy suggests R-49 to R-60 for attics across most of the country, R-13 to R-21 for walls, and anywhere from R-13 to R-30 for floors depending on how cold your zone is.
R-value is simply a number for how well insulation slows heat down. Higher is better. And it stacks: if your attic already has R-19 and you add R-30 on top, you end up with R-49.
Using the recommended target for your zone
The country is split into eight zones, numbered 0 to 8 — 0 is the hottest, 8 the coldest. The colder your zone, the higher the number you want.
Type your state into the R-value insulation calculator here and it picks your zone and sets the target for you. For most people that’s the right choice, because it takes out the step where things go wrong.
One thing worth knowing: those Department of Energy figures are advice, not law. Your local building rules set a separate minimum, and it’s usually lower. Meeting the local rule is the bare minimum. The DOE number is the one that actually pays you back on your bills.
What is the R-value of 10 inches of insulation?
Ten inches of blown cellulose is about R-35. Ten inches of blown fiberglass is about R-25. Those are the figures this calculator works from — 3.5 per inch for cellulose, 2.5 for blown fiberglass.
Published ranges run a little wider on both, because density and product vary: roughly 3.2 to 3.8 per inch for cellulose, and 2.2 to 2.9 for blown fiberglass. So ten inches can land anywhere from R-32 to R-38, or R-22 to R-29. We work from the middle of each range rather than the best case, so an estimate errs toward buying enough.
Same thickness, different results — because every material gives you a different amount of R-value per inch. That’s the whole reason switching material changes how thick the job has to be.
So depth on its own doesn’t tell you much. Check any thickness against any product on our R-value chart by material, and against the figure printed on the bag.
Insulation Calculator by Area: Ceilings, Floors, Crawl Spaces and Basements
Every part of the house wants a different material and a different amount. Attics take loose-fill at R-49 to R-60. Walls take batts or blown-in at R-13 to R-21. Crawl spaces and basements usually take rigid board at R-10 to R-19.
Think of your house as having a shell — everything that separates the warm rooms from the cold outside. Insulation goes on that shell. But each part of it is a different job: different access, different damp risk, different room to work in.
Ceiling insulation calculator
If there’s a cold attic above the ceiling, it’s the same job as the attic floor — just approached from the other side.
If there’s a heated room above, it’s a different thing entirely. There’s no heat escaping, so you’re not insulating for warmth — you’re insulating for noise. Choose mineral wool and don’t worry about the R-value target.
Floors and crawl spaces
A floor over a cold crawl space or basement swings hard with climate: R-13 in the warmest states, R-25 through the middle of the country, and R-30 in the coldest. The calculator sets it from your state, which beats assuming one figure covers everyone.
One rule catches everybody whatever the target: insulation under a floor has to be held up. It won’t stay put on its own. If it’s sagging away from the subfloor, it’s barely doing anything.
Crawl spaces give you two choices, and they’re not the same job:
- Insulate the floor above it and leave the crawl space open to outside air, or
- Insulate the crawl space walls, which brings the whole space inside your warm shell.
The second is usually the better call, especially anywhere humid.
Basement walls
Choose rigid board here — and the reason is damp, not warmth. Basement walls sit against soil that’s always a bit wet. Anything that soaks up water and holds it against the foundation causes a worse problem than the one you were fixing. Rigid board doesn’t mind the moisture. Targets run R-10 in the warm states up to R-19 in the cold ones.
Garages and the gap around the floor
A garage is only worth insulating where it touches heated space: the shared wall, and the ceiling if there’s a room over it.
While you’re down there, check the rim joist — the strip of framing around the outside where the floor meets the foundation. It’s one of the draftiest parts of most houses, and one of the most commonly forgotten.
Attics and outside walls
Attics take more insulation than anywhere else, usually loose-fill blown over whatever’s already there. Because it settles once it’s blown, the math needs an extra step — our attic insulation calculator handles it.
Outside walls take batts, rolls or blown-in, sized to the gap between the framing. Enter the cavity you actually have, because a 2×4 wall caps out well below a 2×6.
What Does This Insulation Calculator Estimate?
Your estimate covers the material, the crew to fit it, and the prep work around it — and stops there. Repairs, permits and clearing out ruined insulation are quoted separately.
| In your estimate | Quoted separately |
|---|---|
| The material itself | Repairs to the roof or structure |
| The crew to install it | Permits and inspections |
| Prep work — sealing drafts, fitting vents at the eaves, boxing around recessed lights | Clearing out wet, moldy or pest-damaged insulation |
| Quantity rounded up to whole packages | Ductwork and ventilation upgrades |
That prep row is worth a second look. It’s the line most estimates leave out. On an attic that needs vents fitted and recessed lights boxed in before anything gets blown, it’s the difference between insulation that works and insulation that just looks like it should.
The other limit is one no tool gets around: it can’t see your house. It doesn’t know your attic is only eighteen inches high at the peak. Or that the only way in is through a bedroom closet. Or that the last crew never fitted the eave vents. Those change how long the job takes, and we find them when we come and look.
So treat the result as a starting figure to plan around, not a shopping list to order from. It’s built from the same numbers our estimators use.
The Insulation Formulas Our Estimator Uses
Five short steps, and that’s the whole calculation. Useful if you’d rather check it yourself — or check somebody else’s quote.
Step 1 — Work out the real surface area
Measure the space, then take off the bits you’re not covering: doors and windows on a wall, the hatch on an attic floor.
Step 2 — Take off what you already have
If there’s insulation up there already, you only pay for the difference.
R-19 already in the attic and an R-49 target means you’re buying R-30, not R-49.
Step 3 — Work out how thick it needs to be
Divide how much insulation you want by how much one inch of that material gives you.
An R-38 target with a material that gives 3.8 per inch needs 10 inches. The same target with a weaker material — say 2.6 per inch — needs nearly 15. That’s why the thickness jumps when you switch material.
Step 4 — Work out how many packs
Divide your area by the coverage printed on the pack, then round up.
Always round up. Coverage is printed on every bag, bundle and roll, and it changes with the R-value — so read it off the pack you’re actually buying.
Step 5 — Add up the price
Prep is small next to the other two, and it’s the one part the first four steps can’t reach — it depends on what we find, not on what you measured.
The insulation estimator above runs all five in order, rounding the pack count up at the end.
Insulation Cost Calculator: How We Price Each Material
Switch the material and the price moves further than the quantity does. Closed-cell spray foam runs three to five times a batt job for the same R-value — because you’re buying draft-proofing as well as insulation.
The insulation cost calculator here gives you a range rather than one figure, because the honest answer to “what will this cost” is a range until someone’s been out to look.
Which insulation types cost more
Comparing shelf prices doesn’t help much — the materials are sold in different units and do different amounts per inch. The fair comparison is what you pay for each unit of warmth, over each square foot. On that basis the order barely changes anywhere in the country.
| Material | Costs this much more than batts | What you get for it |
|---|---|---|
| Batts and rolls | 1× — the baseline | — |
| Loose-fill | 1.1× to 1.4× | Goes over beams and old insulation without disturbing them |
| Mineral wool | 1.5× to 2× | Better against fire and noise |
| Rigid board | 2× to 3× | One unbroken layer, and it copes with damp |
| Open-cell spray foam | 2.5× to 3.5× | Seals drafts in the same pass |
| Closed-cell spray foam | 3× to 5× | Seals drafts, blocks damp, does the most per inch |
These are ratios, not prices — use them to compare materials, not to set a budget. Your own numbers come from the calculator above, which prices each material directly and adjusts for your state.
Two things push the installed price beyond the material. The crew is usually about half the total, and it goes up when the space is awkward to get into. And prep varies a lot — an attic needing vents and boxing before anything gets blown costs real money that a material-only sum never sees.
Why a spray foam quote comes in three times higher
We quote all of these, and the gap catches people out every time.
A foam quote isn’t the same product with a bigger number on it. It includes sealing the drafts, which is normally a separate job.
In a lot of houses that matters more than the insulation does — a well-insulated house with gaps in it still loses heat through the gaps. Foam also does the most per inch of anything on the list, so it’s often the only thing that fits when the space is shallow. Three jobs, one visit.
Whether it’s worth it depends where you’re putting it. In an open attic with plenty of headroom, usually not. In a narrow wall, around the floor edge, or in a crawl space, often yes.
Pricing a foam job specifically? Foam is quoted by the board foot, not the square foot, so it needs its own arithmetic — our spray foam insulation calculator works in that unit and returns the crew hours as well.
Want the actual numbers? Our cost guides go further than this page should: attic insulation cost, blown-in insulation cost, spray foam insulation cost, and fiberglass insulation cost.
Insulation Calculator Examples: Three Worked Estimates
Three real projects, start to finish — what went in, what the math did, and what came out.
The same steps every time, so you can follow the pattern on your own job.
Example 1 — Crawl space walls
What we told it: crawl space walls · 140 ft around the outside · 3 ft high · rigid board · R-10
- Area: 140 ft × 3 ft = 420 sq ft
- Thickness: R-10 ÷ 5 per inch = 2 inches
- Packs: 420 ÷ 32 sq ft per sheet = 13.1, rounded up
14 sheets
Example 2 — Basement walls
What we told it: basement walls · 130 ft around · 8 ft high · two windows and a door · rigid board · R-15
- Area: (130 ft × 8 ft) − 60 sq ft of openings = 980 sq ft
- Thickness: R-15 ÷ 5 per inch = 3 inches
- Packs: 980 ÷ 32 sq ft per sheet = 30.6, rounded up
32 sheets
Example 3 — A whole house shell
This is the one no single-material tool will do for you, and the reason this page exists. Three spaces, three materials, one total — batts here at about 48 sq ft per bundle.
- Crawl space walls — 420 sq ft, rigid board, R-10 → 420 ÷ 32 = 13.1 → 14 sheets
- Floor above it — 1,500 sq ft, batts, R-25 → 1,500 ÷ 48 = 31.3 → 32 bundles
- Garage ceiling — 400 sq ft, batts, R-30 → 400 ÷ 48 = 8.3 → 9 bundles
These are the rounded-up figures, before the extra you’d normally buy for offcuts. Bundle coverage changes with the product and the R-value, so check the package before you order.
What Changes Your Insulation Estimate?
Six things move the number. How much insulation you want, which material you pick, and what’s already up there move it most.
| What you change | What happens |
|---|---|
| How much insulation you want | The biggest lever by far. Going from R-30 to R-49 adds roughly 60% more material |
| Which material | Changes the thickness and the number of packs for the same result |
| What’s already there | You only pay for the difference. R-19 already up there and an R-49 target means you’re buying R-30 |
| How you measured | Counting the doors and windows or not can swing a wall by 15–20% |
| How easy it is to get in | Adds time, not material. Low headroom, one small hatch, or a long carry all cost |
| How deep the gap is | Caps what you can fit, and pushes you toward a material that does more per inch |
The first four change how much you buy. The last two change what it costs to fit. That’s why a shopping list and a contractor’s quote can look different even when the amount of insulation is identical.
Insulation Calculator FAQs
How accurate is an insulation calculator?
The quantity is within about 5% if you measured right — it’s straightforward arithmetic. The price is a range, not a figure, because access and condition vary too much to guess from a screen. Trust the quantity; treat the price as a budget bracket.
Is R-30 enough for an attic?
Not in most of the country. R-30 is below the national recommendation everywhere except the warmest states — so it can pass your local rules and still leave money on the table. Put R-30 in as what you already have, and the tool works out the top-up. Depth, settling and bag counts are on our attic and blown-in calculator.
How much does it cost to insulate a 20x20 room?
A 20 × 20 room has 400 sq ft of ceiling and about 640 sq ft of wall, so it depends which surfaces you’re doing. Run each one through the tool above, then see our attic insulation cost guide for real figures.
Do I need to remove old insulation first?
Usually not. Loose-fill goes straight over most of what’s already there, and taking out insulation that’s dry and undisturbed costs money without buying you anything. Do take it out if it’s wet, moldy, pest-damaged or fire-damaged. Whatever you put on top should be unfaced, for the reason in the materials section above.
How do I figure how much insulation I need?
Measure the surface, take off the doors and windows, pick your R-value, then divide by whatever coverage figure is on the packaging. Round up. The calculator here does all four for you — then buy a little over that number, because offcuts and mistakes are part of every job.
What if my attic already has some insulation?
Enter what’s there and the tool takes it off your target. R-19 already up there with an R-49 goal means you’re buying R-30, not R-49.
Does the calculator work for DIY?
Yes. Choose DIY and it shows material only, with no crew cost. The amount is exactly the same either way.
Is this calculator free?
Yes — no signup, no email, no download. Use it as often as you like.
More Insulation Calculators and Guides
This page gives you a starting estimate. The pages below go deeper on one material or one space, using details this page doesn’t ask for:
- Blown-in and attic insulation calculator — bags, and how deep to blow it so it settles right
- Spray foam insulation calculator — board feet, thickness, and how long the crew is on site
- Insulation R-value chart — R-value per inch for every common material
- Spray foam insulation cost — open-cell and closed-cell, priced by board foot
- Fiberglass insulation cost — batts, rolls and blown, priced per square foot
Doing more than one space? Start here — the totals add up across the whole house as you go.