What is the cost per square foot to build a house?

This site publishes no rate, and the reason is that the number is not a property of a building. It is a ratio whose denominator is undefined: builders quote against heated area, area under roof or footprint according to habit, and on an ordinary house with a garage those differ by about 20%.

What area is cost per square foot usually based on?

Heated or finished area is the usual convention for a house, excluding the garage, covered porches and unfinished basement. Area under roof is a larger number and gives a flattering rate, which is why it turns up in advertising more than in contracts.

Why does a long narrow house cost more per square foot?

Because most of what costs money is priced by the foot rather than the square foot: footings, foundation, wall framing, sheathing, siding, soffit, gutters and roof edge. A 20 by 100 footprint has 34% more perimeter than the same area laid out square, and buys 34% more of all of it.

Is a two storey house cheaper per square foot than a single storey?

Usually yes, because the second floor shares the foundation and the roof with the first and gets both for nothing. It adds a floor structure, exterior wall and a stair. That is why a rate taken from one is misleading for the other.

Why do small houses cost more per square foot?

Fixed items. The permit, the service connections, the kitchen, the bathrooms, the heating plant and the stairs cost much the same whatever the floor area, so they divide by a smaller number. A 1,200 sq ft house is typically about four fifths the cost of an 1,800 sq ft one, not two thirds.

How much exterior wall does a house have?

On a typical two storey house, roughly as much exterior wall as floor area. A 30 by 50 two storey with 9 ft walls has 2,880 sq ft of exterior wall for 3,000 sq ft of floor, which is why anything that lengthens the perimeter is expensive.

What should I ask a builder who quotes per square foot?

Which area they divided by, and what is included. Those two questions resolve most of the apparent difference between quotes, and a builder who cannot answer the first one quickly is not estimating carefully.

Home › Estimating › Cost Per Square Foot Calculator

Cost Per Square Foot Calculator

A ratio with an undefined denominator, and the perimeter it hides

Cost per square foot is the most quoted and least reliable number in construction, and there are two reasons. The denominator is never stated, so the same building divides three different ways. And most of what costs money is priced by the foot, not the square foot, so a long thin house genuinely costs more per square foot than a square one of identical area.

Square foot cost, decomposed

Footprint width

Footprint length

Storeys

no.

Wall height per storey

Quoted against

Garage

sq ft

Covered porch and deck

sq ft

Your rate (optional, $/sq ft)

This site publishes no rate. Enter yours, and the page shows what it is being divided by and what it is hiding.

Specification summary

Generated from on . Reopen that address to reproduce these figures exactly.

Entered

Result

Same floor area, different amount of outside wall

Worked example

A 30 ft by 50 ft two-storey house with a 400 sq ft garage and a 200 sq ft covered porch, 9 ft walls.

Three denominators. Footprint 1,500 sq ft. Heated 3,000. Under roof 3,600. Same house.
The spread. A rate quoted on 3,000 and applied to 3,600 is 20% out, and nobody in the conversation has said a wrong thing.
Perimeter. 160 ft, against 155 ft if the same footprint were square. Only a 3% shape penalty: this plan is reasonably compact.
Make it 20 x 75 instead. Same 1,500 sq ft, but 190 ft of perimeter, a 23% penalty on every trade priced by the foot.
Wall area. 2,880 sq ft of exterior wall for 3,000 sq ft of floor: near enough one to one, which surprises people.

The last line is the useful intuition. On a typical two storey house you build roughly as much exterior wall as you build floor, so anything that lengthens the perimeter is expensive in a way the floor area never shows.

The formula

The arithmetic is trivial. The definitions are the whole problem:

rate = cost / area perimeter = 2(w + l) compact = 4√(wl) penalty = perimeter / compact − 1

area: one of three: footprint, heated, or under roof. Nobody says which
perimeter: the exterior wall length, which is what the by-the-foot trades scale with
compact: the perimeter the same area would have if it were square: the theoretical floor
penalty: how much extra outside wall your shape buys you

A square is the most efficient rectangle: for a fixed area, nothing rectangular has a shorter perimeter. Every departure from square costs exterior wall, and the penalty grows fast. A 20 by 100 house has 34% more perimeter than a square of the same area.

Why this page has no rate on it

Every other page answering this question leads with a number: so many dollars per square foot, national average. This site publishes no price of its own anywhere, and cost per square foot is the figure where publishing one would be least defensible.

It is not a property of a building. It is a ratio, and both halves are unstable. The numerator varies with specification, labour market and season. The denominator is not even defined: builders quote against heated area, area under roof or footprint according to habit, and the spread between them on an ordinary house with a garage is twenty percent.

So what a calculator can honestly do is show you the denominators side by side, apply your own rate to each, and surface the physical quantities the rate is standing in for. That is what this page does.

The perimeter point is the one worth taking away. Foundation, framing, sheathing, siding, insulation, roof edge, gutters, flashing: all priced by the foot. A long thin plan buys more of every one of them for the same floor area, and no rate card carries a shape adjustment.

The three denominators, and what each one is for

Heated area, sometimes called conditioned or finished area, is the usual convention for a house price and the one most builders mean. It excludes the garage, the covered porch and unfinished basement.

Area under roof includes everything the roof covers. It is a larger number, so the same total divided by it gives a lower rate, which is why it appears in advertising more often than in contracts.

Footprint is the ground floor only. On a two storey house it is half the heated area, so a rate quoted against it is roughly double. It is used for site and foundation work, where it is the right denominator.

Gross versus net is the same trap the occupant load calculation sets, and it catches people the same way: the arithmetic is easy and the definition is where the answer is actually decided.

What scales with area and what scales with perimeter

By the square foot: flooring, drywall, ceiling, insulation in the flat planes, roof covering, slab concrete, paint on ceilings.

By the linear foot: footings, foundation wall, sill plates, exterior wall framing, sheathing, housewrap, siding, corner boards, soffit, fascia, gutters, roof edge, flashing.

Fixed regardless of size: the permit, the connection to services, the kitchen, most of the bathrooms, the heating plant, the stairs. These are why small houses cost so much per square foot: the fixed items divide by a smaller number.

That third group is the reason a 1,200 sq ft house is not two thirds the cost of an 1,800 sq ft one. It is usually closer to four fifths.

Why a second storey is cheaper per square foot

The second floor of a two storey house shares the foundation and the roof with the first. Those are two of the most expensive assemblies in the building and the second storey gets both for nothing.

What it adds is a floor structure, exterior wall, and a stair. On most plans that is genuinely cheaper per square foot than extending the footprint, which would need more footing, more slab and more roof.

The practical consequence is that a per-square-foot rate taken from a single-storey project is misleading for a two-storey one and the other way round. If you are given a rate, ask what it came from.

Frequently asked questions

What is the cost per square foot to build a house?: This site publishes no rate, and the reason is that the number is not a property of a building. It is a ratio whose denominator is undefined: builders quote against heated area, area under roof or footprint according to habit, and on an ordinary house with a garage those differ by about 20%.
What area is cost per square foot usually based on?: Heated or finished area is the usual convention for a house, excluding the garage, covered porches and unfinished basement. Area under roof is a larger number and gives a flattering rate, which is why it turns up in advertising more than in contracts.
Why does a long narrow house cost more per square foot?: Because most of what costs money is priced by the foot rather than the square foot: footings, foundation, wall framing, sheathing, siding, soffit, gutters and roof edge. A 20 by 100 footprint has 34% more perimeter than the same area laid out square, and buys 34% more of all of it.
Is a two storey house cheaper per square foot than a single storey?: Usually yes, because the second floor shares the foundation and the roof with the first and gets both for nothing. It adds a floor structure, exterior wall and a stair. That is why a rate taken from one is misleading for the other.
Why do small houses cost more per square foot?: Fixed items. The permit, the service connections, the kitchen, the bathrooms, the heating plant and the stairs cost much the same whatever the floor area, so they divide by a smaller number. A 1,200 sq ft house is typically about four fifths the cost of an 1,800 sq ft one, not two thirds.
How much exterior wall does a house have?: On a typical two storey house, roughly as much exterior wall as floor area. A 30 by 50 two storey with 9 ft walls has 2,880 sq ft of exterior wall for 3,000 sq ft of floor, which is why anything that lengthens the perimeter is expensive.
What should I ask a builder who quotes per square foot?: Which area they divided by, and what is included. Those two questions resolve most of the apparent difference between quotes, and a builder who cannot answer the first one quickly is not estimating carefully.

Check these numbers yourself

ANSI Z765, Square Footage Method for CalculatingHome Innovation Research Labs, which administers the standard. ANSI Z765 exists precisely because finished square footage is otherwise ambiguous, and it is the reason a measured area can be argued about at all. The standard itself is a paid document.
NAHB housing economicsNational Association of Home Builders. Its periodic cost of construction surveys break a build down by trade share, which is the honest way to reason about a per-square-foot figure rather than quoting one.

How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.

Figures on this page last checked against the source documents on 2026-09-08. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

No rate is published here. Cost per square foot is a ratio with an undefined denominator and it is not a property of a building. The rate field is yours to fill. Quantities on this page are geometry from your dimensions and assume a simple rectangular footprint.