Square Footage Calculator

What Is Square Footage?

Area is, in Wolfram MathWorld's phrasing, the amount of material needed to cover a surface completely. Square footage is that quantity counted in square feet, and the reason it dominates American building and property work is that almost everything you buy for a floor is priced by it.

Buying planks or boards from this figure? The waste allowance, the box count and the layout math live in the Flooring Calculator.

Square Footage, Defined

One square foot is a square measuring one foot on each side. Square footage is how many of those squares fit inside a boundary. A 12 ft by 15 ft bedroom holds 180 of them, so its area is 180 square feet — and that is true whether the room is carpeted, tiled or bare, because area describes the space, not what is in it.

MathWorld gives the rectangle its one-line formula, A = ab, where a and b are the side lengths. That is the whole of the arithmetic on this page. Everything else here is either converting your tape-measure units into feet first, or converting the answer into some other area unit afterward.

The unit is written several ways and they all mean the same thing: sq ft, sqft, ft², and the trade shorthand SF. Real-estate listings often say GLA, gross living area, which is square footage measured under a specific rulebook — that distinction gets its own section further down, because it is the single most common reason two people measuring the same house get two different numbers.

Square Feet, Square Yards, Square Meters and Acres

The calculator prints four area units because different trades buy in different ones. The conversions between them are fixed, and all but one are exact rather than approximate:

• Square foot (sq ft) — the output unit, and the one flooring, tile, paint coverage, drywall and per-square-foot pricing are quoted in.
• Square yard (sq yd) — 9 sq ft, because a yard is 3 feet and 3 × 3 = 9. Carpet, and broadloom in particular, is still sold this way. Enter 1 × 1 yd and the tool returns 9 sq ft; enter 36 × 36 in and you get the same 9 sq ft.
• Square meter (m²) — 1 sq ft is exactly 0.09290304 m², a value NIST publishes in boldface to mark it as exact rather than rounded. Going the other way, 1 m² is 10.7639 sq ft: enter 1 × 1 m and the result reads 10.76 sq ft.
• Acre — 43,560 sq ft, which is 4,046.86 m². Enter 220 × 198 ft and the acre line reads 1.000 acres; enter 660 × 660 ft and it reads 10.000 acres.

The square-meter factor comes straight out of one exact definition: the international foot is exactly 0.3048 m, so a square foot is exactly 0.09290304 m². The 9 sq ft to the square yard and the 43,560 sq ft to the acre are exact by definition too. One constant here is not exact — the meters-to-feet factor the calculator converts with, 3.280839895, is 3.2808398950131… truncated, which pulls a metric entry short by under one part in a billion. It never shows at two decimals, but the meter path is the one place a rounded number enters the chain.

What This Calculator Returns

One headline figure and two supporting lines. A 12 × 15 ft room returns 180 sq ft as the headline, then = 20 sq yd = 16.72 m², then an echo of the entry, 12 × 15 ft. What is on the page is exactly that:

• The total in square feet, with thousands separators and up to two decimals — 1,200 sq ft for a 30 × 40 ft footprint, 134.38 sq ft for a room measured at 150 × 129 in.
• The same area in square yards and square meters, always.
• Acres, but only from 2,178 sq ft upward. That cutoff is one twentieth of an acre exactly: 2,177 sq ft shows no acre figure, 2,178 sq ft shows 0.050 acres.
• A restatement of what you typed, including the section count when it is above one — 3 sections of 12 × 10 ft.
• No cost, no material quantity, no waste allowance, no box or bag count, no perimeter, no volume, no unit price of any kind.

Nothing is added to the geometry and nothing is deducted from it. The number is the area of the rectangle you described, which is the starting point for a materials order rather than the order itself.

How Do You Calculate Square Footage?

Measure the two dimensions, get them into the same unit, multiply. The work is in the measuring and in the unit handling — the multiplication has never been the hard part.

The Square Footage Formula, Written Out

One multiplication, with a unit conversion in front of it and three unit conversions behind it:

Area = Length × Width

Entered in feet:    Area (sq ft) = L × W
Entered in inches:  Area (sq ft) = (L ÷ 12) × (W ÷ 12)
Entered in yards:   Area (sq ft) = (L × 3) × (W × 3)
Entered in meters:  Area (sq ft) = (L × 3.280839895) × (W × 3.280839895)

Several identical areas:  Area = Length × Width × Sections

Then, from the square-foot total:
  sq yd = sq ft ÷ 9
  m²    = sq ft × 0.09290304
  acres = sq ft ÷ 43,560     (displayed only from 0.05 acres up)

Both dimensions use the same unit selector, so there is no way to enter a length in feet against a width in meters. If your two measurements came off different tapes, convert one of them before you type it in.

Step by Step

• Clear the floor along two adjacent walls, and measure at floor level rather than at waist height — baseboards and bowed drywall make the two readings differ by an inch or more in older houses.
• Take the length along the longest straight run, wall to wall. Take the width perpendicular to it, again wall to wall.
• Decide on one unit for both readings and set the selector to match. Inches are the most accurate choice for a room, because a tape reads inches directly and nothing has to be converted by hand.
• Enter the length and the width. Both have to be greater than zero — a blank, a zero or a negative returns "Enter a length and width greater than zero" instead of a figure.
• If you are measuring several identical spaces, put the count in the last box. Leave it blank or at 1 for a single area.
• Read the square-foot headline, and take the square-yard, square-meter or acre line if that is the unit your supplier or your paperwork uses.

Two habits are worth building. Measure twice on anything you are about to spend money on, and round up rather than down when a wall is not quite straight — a 6 in wobble across a 12 ft wall is 6 sq ft of flooring, which is real money on the second trip to the store.

Worked Example: a 12 × 15 ft Bedroom

A standard secondary bedroom, worked exactly the way the calculator works it:

• Unit: feet. Length: 12. Width: 15. Sections: left at 1.
• Neither dimension needs converting, so the conversion factor is 1 and the multiplication runs on the numbers as typed.
• Area in square feet: 12 × 15 = 180.
• Square yards: 180 ÷ 9 = 20.
• Square meters: 180 × 0.09290304 = 16.7225, displayed to two decimals as 16.72.
• Acres: 180 ÷ 43,560 = 0.0041, which is below the 0.05 display threshold, so no acre line appears.

12 × 15 ft bedroom — calculator output

180 sq ft = 20 sq yd = 16.72 m²

Measure the same room in inches — 144 × 180 in — and the answer is identical, because 144 ÷ 12 is 12 and 180 ÷ 12 is 15. That equivalence is the point of the unit selector: it removes the hand conversion where the mistakes happen.

Measuring in Inches, Yards or Meters

Inches are the most useful non-foot option, because rooms are rarely a whole number of feet across and a tape gives you inches without arithmetic. Every row below is a calculator output:

Two of those rows are the same room twice. 138 × 162 in and 11.5 × 13.5 ft both return 155.25 sq ft, because 138 ÷ 12 is 11.5 and 162 ÷ 12 is 13.5. The one trap in feet is writing a feet-and-inches reading as a decimal: 12 ft 6 in is 12.5, not 12.6. Enter 12.6 × 10 and you get 126 sq ft where the true figure is 125 sq ft — a foot of floor conjured out of a typing convention.

Totaling Identical Areas in One Run

The last input multiplies the area by a count, which saves running the same two numbers over and over for matched spaces. It is genuinely a multiplier and nothing more — the areas have to be identical for the total to mean anything.

Only the product matters, never the shape it came from: two sections of 12 × 8 ft and six sections of 4 × 8 ft both return 192 sq ft. The count is rounded to the nearest whole number and floored at 1, so 2.6 sections is read as 3 and returns 360 sq ft from a 12 × 10 ft area, while 2.4 is read as 2 and returns 240 sq ft. A blank or a zero in that box is treated as one area.

When the Room Is Not a Rectangle

Two numbers multiplied describe a rectangle, so anything else has to be reduced to rectangles — or to a shape whose area you work out first and then enter as a single dimension against a width of 1.

Rectangle:  A = length × width
Circle:     A = π × r²           (r = half the distance across)
Triangle:   A = ½ × base × height
L-shape:    split into rectangles, run each, add the totals

• L-shaped room: a 20 × 12 ft leg returns 240 sq ft and a 12 × 8 ft leg returns 96 sq ft, so the room is 336 sq ft. Enter 336 × 1 ft to confirm it and you get 336 sq ft back.
• Circular patio 12 ft across: r is 6 ft, so A = π × 36 = 113.1 sq ft. Enter 113.1 × 1 ft and the calculator converts it for you — 12.57 sq yd, 10.51 m².
• Triangular garden bed with a 10 ft base and 8 ft height: A = ½ × 10 × 8 = 40 sq ft, which enters as 40 × 1 ft and returns 4.44 sq yd, 3.72 m².
• Bay window, alcove or chimney breast: measure it as its own small rectangle and add it to, or subtract it from, the main figure before ordering.

Splitting a room costs almost nothing in accuracy. Add the two L-shape legs in square meters — 22.3 plus 8.92 — and you get 31.22 m², precisely what the single 336 sq ft run returns. In square yards the two-run total is 37.34 against 37.33 for the single run, a one-hundredth of a square yard that came from rounding each leg to two decimals before adding. Add the areas first where you can; it is marginally cleaner and it is one less number to copy down.

Square Footage Chart for Common Rooms and Lots

Every figure in these tables is this calculator's own output for the dimensions shown, not a rounded approximation.

The pattern worth internalizing: doubling one dimension doubles the area, doubling both quadruples it. A 10 × 10 room is 100 sq ft and a 20 × 20 room is 400 sq ft, not 200 — which is why a room that looks twice the size costs four times as much to floor.

Metric Room Chart

Metric entries are converted to feet first, multiplied, and then converted back, so the square-meter column lands on the number you would expect while the square-foot column carries the conversion:

A 20 × 20 ft garage and a 6.096 × 6.096 m garage are the same building: both return 400 sq ft and 37.16 m². That is the exact-foot definition doing its job — 6.096 m is 20 ft to the millimeter.

Lot Sizes and When Acres Appear

Land is where the fourth unit switches on. The acre line is suppressed below 0.05 acres — 2,178 sq ft — because a three-decimal acre figure is meaningless for a bedroom:

The acre in its original form is one chain by one furlong — 66 × 660 ft — and the 220 × 198 ft row is that same 43,560 sq ft drawn as a different rectangle. The exact figure is why a quarter-acre lot is 10,890 sq ft and an eighth is 5,445.

House Square Footage Follows a Different Rulebook

Add up every room in a house and the total will not match the figure on the listing. Neither number is wrong — they are measuring different things, under different rules, for different purposes.

What an Appraiser Actually Measures

For a mortgage appraisal in the United States the method is not a matter of preference. Fannie Mae's Selling Guide states that appraisers must follow the American National Standard Institute Square Footage-Method for Calculating: ANSI Z765-2021 when measuring, calculating and reporting the above- and below-grade square footage of a single-family dwelling. That requirement took effect for appraisals with effective dates from April 2022.

The standard's rules are stricter than a tape across a floor. As summarized by the Wisconsin REALTORS Association, finished areas must have a ceiling height of at least 7 feet; in a room with a sloping ceiling at least 50% of the finished square footage must be at least 7 feet high, and no part of the room below 5 feet counts at all. Measurements of each level are taken to the exterior finished surface of the outside walls, readings are made to the nearest inch or tenth of a foot, and the final figure is reported to the nearest whole square foot.

Below-grade space is separated out rather than added in. Fannie Mae considers a level to be below-grade if any portion of it is below-grade, regardless of the quality of its finish or the window area of any room — so a fully finished walk-out basement is reported as basement area, not as living area, and a garage is not living area either.

Why the Room Totals Never Add Up

Exterior measurement is the main gap. A house with a 30 × 40 ft footprint is 1,200 sq ft measured to the outside of the walls. Take 6 inches of wall thickness off each side and the interior envelope is 29 × 39 ft, which this calculator returns as 1,131 sq ft — 69 sq ft, or 5.75%, that exists in the listing figure and not in any room.

Interior partitions widen the gap further, because every stud wall inside the house sits in space the exterior measurement already counted. Stairs get a rule of their own: in the Wisconsin REALTORS summary of the standard, a staircase is included in the gross living area of the floor from which it descends — counted on that one level, not on every level it passes through. Add up bedrooms alone and you will land far below the listed number even before the wall thickness is accounted for.

None of which makes room-by-room measurement useless — it is the right method for the job it is for. You floor a room, paint a room and tile a room, so a room-by-room total is what you order from. The listing figure is for valuation and comparison, and it belongs on a different page of the notebook.

How to Read Your Result

Which Line You Need

The headline square-foot figure is what almost every US supplier wants. Flooring, tile, laminate, vinyl plank, sheet goods, turf, decking, drywall, insulation and per-square-foot labor quotes are all priced in it, and it is the figure to write on the back of the tape-measure envelope.

The square-yard line is for carpet, and for concrete or asphalt work quoted by the yard. A 9 × 12 ft area rug is 108 sq ft, which the calculator also gives as 12 sq yd — the number a broadloom supplier prices from.

The square-meter line is for anything metric: European or Asian product specs, imported tile boxes labeled by m², and coverage rates printed in metric on the tin. A 12 × 15 ft bedroom is 16.72 m², a 30 × 40 ft footprint is 111.48 m².

The acre line only appears from 2,178 sq ft upward, and it exists for land. Under three decimal places it can look tidier than it is: a 208.71 × 208.71 ft square returns 43,559.86 sq ft and displays as 1.000 acres, which is 0.14 sq ft short of a true acre.

From Square Feet to a Materials Order

Area is the input to the order, never the order itself. Three steps stand between the two, and only the first is multiplication:

• Price it. Cost = area × price per square foot, using your own quote. At a quoted $4.50 per square foot, the 180 sq ft bedroom is 180 × 4.50 = $810 of material. The same multiplication prices tile, refinishing, cleaning and rent quoted per square foot.
• Add waste. Anything that gets cut — planks, tile, wallpaper, sheet vinyl — needs a cutting allowance on top, commonly around 10% for a straightforward layout and more for diagonal or herringbone patterns and rooms with many jogs. Ten percent on the 180 sq ft bedroom is 198 sq ft, which is what you buy.
• Round to the packaging. Flooring comes in boxes, tile in cartons, mortar in bags. A 198 sq ft requirement met by 22.5 sq ft boxes is nine boxes, because you cannot buy 8.8 of them.

Ordering by the box, with the waste percentage and the carton rounding done for you, is a separate calculation — that one lives in the Tile Calculator.

Paint is the exception to all of it. Paint covers walls, so the floor area is the wrong surface entirely.

Measuring Walls Instead of Floors

For paint and wallpaper the two dimensions are a wall's width and its height, and the identical-areas box becomes genuinely useful because opposite walls match. Take the 12 × 15 ft bedroom with a 9 ft ceiling: two sections of 12 × 9 ft returns 216 sq ft, two sections of 15 × 9 ft returns 270 sq ft, and the room's walls total 486 sq ft.

Then subtract the openings, because you are not painting them. A 3 × 7 ft door is 21 sq ft and a 3 × 5 ft window is 15 sq ft, so 486 − 21 − 15 leaves 450 sq ft of wall — 41.81 m², if the coverage rate on your tin is metric. Skipping that subtraction overstates the job by 8%: 36 sq ft of openings against the 450 sq ft you would actually be painting.

Ceilings go back to floor math: the ceiling of that room is the same 180 sq ft as its floor. Add it to the wall figure only if you are painting it in the same color, and keep it separate if you are not.

Limits: When This Calculator Does Not Apply

The honest boundary of one length multiplied by one width:

• Any shape that is not a rectangle, until you have done the area yourself. Circles, triangles, trapezoids and irregular lots have their own formulas; this tool multiplies whatever two numbers you hand it.
• Rooms with jogs, alcoves, bays or angled corners. Split them into rectangles and run each one — the calculator holds a single shape at a time and has no running total.
• Sloped surfaces. A roof plane, a ramp or a hillside covers more material than its footprint, and the plan dimensions understate it. Measure along the slope, or work from the pitch.
• Volume of any kind. Concrete, mulch, gravel and soil need a depth as well, and no depth is asked for here.
• Listing or appraisal square footage, which follows ANSI Z765-2021 rules on ceiling height, exterior measurement and below-grade space rather than a tape across a floor.
• Very small inch entries. A 1 × 1 in square returns 0.01 sq ft, and the square-yard and square-meter lines both round to 0 at that size.
• Cost, materials and waste. No prices, coverage rates or allowances are built in — and none should be, because those are local, they vary by product, and they go stale.

Two of those — sloped surfaces, and the listing rulebook — are limits of the method itself, true of any tape and any tool. The rest are things this calculator does not attempt. None is a reason to distrust the number; they are the list of things the number was never measuring.

Where the Rounding Shows

The square-foot headline carries two decimals, which is finer than any tape measure justifies. A room read to the nearest inch is already carrying about a third of a percent of uncertainty on a 12 ft wall, so 134.38 sq ft and 134 sq ft are the same measurement in every way that matters to an order.

The secondary lines round to two decimals each, which is why adding two separate runs can land a hundredth away from running the combined area once — 37.34 sq yd against 37.33 for the L-shaped room above. The acre line rounds to three decimals, which can round a shortfall out of sight at 1.000 acres.

The larger error is always upstream of the arithmetic. A wall measured at waist height instead of floor level, a decimal written as 12.6 when the tape said 12 ft 6 in, or a bay window left out of the sketch will each move the answer further than every rounding in the calculator put together.

Working with land rather than rooms, and want hectares and square rods alongside the acres? That conversion set is in the Acreage Calculator.