Insulation calculator

How much does insulation cost?

Insulation is priced per square foot, but the number that actually determines your cost is the R-value gap, the difference between what you have now and what your climate zone calls for. Insulating 1,200 square feet from R-19 to R-49 costs $2,784; closing the whole gap from bare joists on the same attic costs $3,787. Identical area, very different bill.

Across the common materials, installed cost runs roughly $2,456 to $9,471 for that same 1,200 square foot attic upgrade, a 4x spread driven almost entirely by material choice. Doing the work yourself removes the labor line, which is 40-60% of a professional job and brings the blown-in version to about $1,704.

The calculator above starts from your state's DOE climate zone, looks up the recommended R-value for the assembly you are insulating, subtracts what you already have, and prices only the difference. That is a materially different approach from calculators quoting a flat per-square-foot price regardless of where you live or what is already up there.

A free insulation calculator: enter your square feet

This is a free insulation calculator in the ordinary sense of the word, no email address, no phone number, no account, and no handing your project details to three contractors who will call you for a fortnight. Enter your square footage, pick the area you are insulating, tell it roughly what is already there, and you get an itemized estimate. Close the tab if that is all you needed.

Square feet means the floor area of the space, not the roof surface above it: for an attic, the footprint of the rooms below. If you do not know what R-value you already have, measure the depth of the existing material in inches and divide by roughly 3. It is approximate, but far better than guessing, and the calculator offers the common presets from bare joists up to R-38.

Every line is shown separately, material, waste allowance, installation labor and equipment rental, because a single bottom-line figure is not much use when you are deciding between batt and blown-in, or between hiring the job out and renting a blower. The formula is documented on this page rather than hidden, and the labor line comes from Bureau of Labor Statistics construction earnings data for your state rather than an invented regional percentage.

Attic insulation: R-value by climate zone

The attic returns more per dollar than any other assembly in almost every US climate, which is why this attic insulation calculator opens on it by default. Heat rises, the ceiling plane is riddled with penetrations, and access is easier than anywhere else in the envelope. The DOE target runs from R-30 in zone 1 to R-49 across zones 4 through 7.

In depth, R-49 is 14 inches of blown-in cellulose, 19.6 inches of blown fiberglass or 15.3 inches of fiberglass batt. Blown-in is sold against a coverage chart that shrinks as depth rises, a bag covering 32 square feet at R-30 covers only about 20 at R-49, so a 1,000 square foot attic taken to R-49 needs roughly 52 bags, not the 31 the R-30 chart implies.

Size and zone move the total together. A 2,000 square foot attic insulated from scratch costs about $6,312 nationally, $5,132 in Texas where zone 2 asks for R-38, and $6,470 in Minnesota where zone 6 asks for R-49. Two details protect that investment whatever you spend: baffles keeping material off the soffit vents, and air sealing the ceiling plane before anything is laid over it.

Blown-in vs batt vs spray foam

Fiberglass batt is the cheapest way to hit an R-value on paper, $2,456 for the reference attic, and the least forgiving in practice. It loses most of its rated performance when compressed or fitted with gaps around wiring and boxes, and those gaps are extremely common in real installations. It suits clean, evenly spaced joist bays and a patient installer.

Blown-in solves exactly that problem by flowing around obstructions, which is why it dominates attic retrofits. Use the blown in insulation calculator setting and you can compare the two loose-fill options directly: cellulose at $2,784 and R-3.5 per inch, against blown fiberglass at $3,101 and R-2.5. The cellulose insulation calculator figure is usually the better value in an open attic, more R per inch, made largely from recycled paper, and it dense-packs into closed wall cavities without opening the wall. Its trade-off is settling, roughly 10-20% over the first few years unless packed to density.

Spray foam is a different product doing a different job. Run the spray foam insulation calculator setting and the same attic comes to $6,616 in open-cell or $9,471 in closed-cell, several times the cost of loose fill. What you buy is R-6.5 per inch and an air barrier in one operation, which is decisive in a vaulted ceiling, a rim joist, a shallow crawl space or a 2x4 wall, and largely wasted on an open attic floor where depth is free. Rigid foam board sits between them at $3,672: R-5 per inch, DIY-installable, and the only practical way to add continuous insulation outside the sheathing where it breaks the thermal bridge through the studs.

Wall insulation options and costs

Exterior walls are the largest surface in the building envelope and the hardest to retrofit, which is why they come second to the attic rather than first. Insulating 1,500 square feet of bare exterior wall to the zone 4 recommendation of R-13 costs about $1,755 in fiberglass batt where the wall is already open, or $2,358 dense-packed with cellulose through bored holes in a finished house.

Cavity depth is the binding constraint and it does not negotiate. A 2x4 stud bay gives you 3.5 inches, which holds R-13 to R-15 in fiberglass; R-19 batts are sized for 2x6 framing and deliver only about R-13 once squashed into a 2x4 wall, so you pay for R-19 and receive a third less. Closed-cell foam at R-6.5 per inch is the only material reaching R-22.75 in that space.

Set the area selector to exterior walls and the wall insulation calculator applies your zone's target, from R-13 in the far south to R-21 in the coldest counties. One thing worth knowing before you commit: interior walls are not worth insulating for energy at all, since both sides are conditioned space. The exceptions are soundproofing, walls shared with an unheated garage, and unit separation in multi-family buildings.

DOE climate zones explained

The Department of Energy divides the US into eight climate zones; the 50 states span zones 1 through 7. Zone 1 covers Hawaii and southern Florida, and zone 7 covers Alaska and the coldest northern interior counties. The zone is a proxy for degree days, zone 2 sees roughly 1,400 heating degree days a year against 7,900 in zone 6, which is what actually drives both the target and the savings.

Attic recommendations range from R-30 in zone 1 to R-49 in zones 4 through 7; walls from R-13 to R-21. The difference between a zone 2 and a zone 6 house is not a detail. It is roughly a 60% swing in required attic R-value, and it is the reason a national average insulation figure tells you almost nothing useful about your own house.

Two caveats on the zone map. Several states straddle two zones, and mountainous counties in California, Arizona and North Carolina sit a zone or two colder than their state figure suggests. And two states set targets above the federal recommendation: California through Title 24 and Washington through the Washington State Energy Code. If you are in either, check the current code cycle before buying material.

What insulation actually saves on energy bills

The Department of Energy estimates that air sealing plus insulation cuts heating and cooling costs by around 15%. Our model is more specific and deliberately more conservative: the 1,200 square foot attic taken from bare joists to R-49 saves about $610 a year and pays back in 6.2 years, while the same attic topped up from an existing R-19 saves roughly $63.

That gap is the most useful thing on this page. Insulation returns diminish sharply, the first few inches eliminate most of the heat flow, and everything after that competes with the air sealing you have not done yet. An uninsulated or barely insulated attic is an easy financial decision; taking an already-compliant attic higher is not.

The savings figure prices heating against a national residential natural gas price and cooling against the residential electricity rate the US Energy Information Administration publishes for your state, currently 17.0¢ per kWh at the national default. It models conduction through the assembly only, ignoring air leakage, duct losses and solar gain, and applies a 70% realization factor to what the physics predicts, so in an older, leakier house the real saving is usually higher than the number shown.

How we calculated these estimates

Every figure on this page comes from the same open formula the calculator above uses. We start from your state's DOE climate zone, look up the R-value the Department of Energy recommends for the assembly you are insulating, subtract the R-value already in place, and price only the gap that is left, which is why two houses of identical size get very different numbers. Depth comes from the material's published R per inch, material cost from a 2026 national baseline per square foot per inch, and a 10% allowance is added for trimming and irregular framing. Installed labor is then scaled by the construction earnings multiplier the Bureau of Labor Statistics publishes for your state. The energy saving is a steady-state conduction estimate priced against real US Energy Information Administration residential electricity rates and a national natural gas price, with a 70% realization factor applied. It deliberately excludes air leakage, duct losses and solar gain, so it is a conservative planning figure rather than an energy audit. Nothing is hidden behind a lead form and no contractor pays to appear here. What this is not is a quote: attic access, obstructions, existing damage and any air sealing or venting work are priced separately by whoever does the job.