Square Footage Calculator

How to calculate the square footage of a rectangle

Run a tape measure along one wall for the length, and along the wall next to it for the width, then multiply the two: length times width gives the square footage, which is also the general answer to how to calculate square footage or how to calculate square feet for any plain rectangular space, once both dimensions are in the same unit. Length and width each carry their own unit dropdown, so a length measured in feet and a width measured in yards can be entered exactly as taped, and the calculator converts before multiplying. For an oddly shaped room, how to figure out square footage usually means splitting it into smaller rectangles first, finding each piece's square footage separately, and adding the pieces together.

Worked example: a living room measures 12 feet long and 10 feet wide. Multiplying the two gives 12 x 10 = 120 square feet, exactly what the calculator shows for a rectangle entered with those measurements. Enter a price and that total is multiplied by it for a total cost: at $5 per square foot, 120 x 5 = $600. Leave the price blank to see the square footage alone.

How to measure square footage of a room

Measure wall to wall along the floor, write each length in feet and inches, and convert the inches to a decimal before multiplying: a wall of 11 feet 6 inches is 11.5 feet, because 6 inches is half a foot. When the floor plan is not a plain rectangle, split it into rectangles, run each one through the Rectangle card and add the results. A closet or alcove that will get the same flooring is one more rectangle, while a fireplace hearth or built-in cabinet that blocks the floor can be measured on its own and subtracted. Measure every dimension twice and round to the nearest inch, since an error of one foot on a 12 foot wall changes the area by about 8 percent.

L-shaped, angled and curved rooms follow the same steps once the floor plan is broken into pieces, and the guide to the square footage of an odd shaped room works through examples of each.

Common room sizes in square feet

The table lists the floor area of common room dimensions in square feet, square yards and square meters, worked out with the same rectangle formula the calculator uses. For scale, 100 square feet is a 10 by 10 room, 400 square feet is 20 by 20, and 1000 square feet is a 25 by 40 rectangle. Carpet is sometimes quoted per square yard, so the middle column saves the division by 9.

How the eight extra shapes calculate area

Four of the eight extra shapes use formulas already proven on this site's Area Calculator: the square feet of a circle is pi times its radius squared, a triangle from base and height is half of base times height, a trapezoid is half the sum of its two parallel bases times the height between them, and a parallelogram is base times height. The other four are new to this page.

Rectangular border. A garden bed edging or a picture mat: the area is the outer rectangle minus an inner rectangle, where the inner length and width are each shrunk by twice the border width. Worked example: a 12 by 10 foot outer rectangle with a 1 foot border gives an inner rectangle of 10 by 8 feet, so 120 minus 80 is 40 square feet of border. A border wide enough to make the inner shape negative is clamped to zero, so an oversized border simply reports the full outer area.

Ring (annulus). The same idea with circles: area is pi times the outer radius squared minus pi times the inner radius squared. A 5 foot outer radius with a 2 foot border gives an inner radius of 3 feet, for pi x (25 - 9), or 16 x pi, about 50.27 square feet.

Sector. A pie-slice wedge of a circle, scaled from the full circle's area by whatever fraction of 360 degrees it covers. A 6 foot radius with a 90 degree angle gives pi x 36 x (90 / 360), or 9 x pi, about 28.27 square feet.

Triangle from three side lengths. Heron's formula finds the area from three edges alone: the semi-perimeter (half the sum of the sides), then the square root of that semi-perimeter times itself minus each side in turn. Sides of 5, 6 and 7 feet give a semi-perimeter of 9 and an area of the square root of 216, about 14.70 square feet. Any side longer than the sum of the other two, like 2, 3 and 10 feet, describes no real triangle and is rejected.

Square footage calculator formulas by shape

Rectangle

Rectangular border

Circle

Ring (annulus)

Sector

Triangle, three side lengths (Heron's formula)

Triangle, base and height

Trapezoid

Parallelogram

Square footage reference conversions

A few conversions come up constantly when comparing square footage against other area units:

• 1 acre = 43,560 square feet
• 1 square yard = 9 square feet
• 1 square foot = 144 square inches
• 1 square meter ≈ 10.7639 square feet
• 1 hectare ≈ 107,639 square feet (about 2.47 acres)

These are the same conversions this calculator's unit dropdown applies on the eight extra shapes: type a dimension in yards, meters or centimeters and the result still comes back in square feet.

Small areas convert by 144, the number of square inches in a square foot. To convert square inches to square feet (sq in to sq ft), divide by 144, and multiply by 144 to go back. A tile that is 15 in square covers 15 x 15 = 225 square inches, or 225 / 144 = 1.5625 square feet, so ten of them cover 15.625 square feet. Larger areas use the square yard: to convert square feet to square yards, divide by 9. The question "how many square feet in a yard" usually means a square yard, which is 3 feet by 3 feet, or 9 square feet, so a 12 x 12 foot room of 144 square feet is 16 square yards.

Converting linear feet to square feet

Linear feet measure length only, so a conversion from linear ft to sq ft needs a width. Multiply the length in feet by the width in feet: 40 linear feet of a board 6 inches wide, which is half a foot, covers 40 x 0.5 = 20 square feet. Going the other way, a sq ft to linear ft calculator just divides the area by the width, so 100 square feet of 6 inch boards takes 200 linear feet before any allowance for waste.

Calculating cost per square foot

Once an area is known, turning it into a cost estimate is one multiplication: total square footage times a price per square foot, which is exactly what makes every shape above double as a cost per square foot calculator and a price per square foot calculator once a rate is entered. Painting is usually quoted this way, with a per-square-foot rate that typically covers one or two coats; a small bedroom is a very different budget than an open-plan living area three or four times the size.

Used as a square foot calculator for flooring, the same rectangle total above is what a flooring quote is built from. Costs vary by material: laminate is usually the cheapest and fastest to install but holds up less well to moisture, solid or engineered wood costs more but lasts longer, and tile's installation labor tends to cost more than either because of cutting and grout work. The arithmetic never changes, area times price per square foot, but the same square footage can lead to very different totals depending on the material priced against it. For a much larger project, like pricing a whole house, a published price-per-square-foot figure is a useful starting range rather than a final number, since land, permits and finishing choices are often priced separately from it.

How this differs from the Area Calculator

This site's Area Calculator is a more abstract, general-purpose geometry tool across eight shapes, with independent per-field unit dropdowns but no quantity or cost built in. This Square Footage Calculator is built for home improvement: every shape converts its own unit into square feet automatically with optional quantity and price fields, so an area turns directly into a project cost estimate.