How to Calculate Square Footage (With Examples)

Contractors and homeowners need this number constantly: for a flooring quote, a paint order, a material takeoff, or a real estate listing. Get it wrong on an L-shaped room, or measure to the wrong wall, and the number you hand a customer can be off by an entire closet's worth of space.

The good news is the math itself is simple. This guide covers the basic formula, how to convert between units, and how to handle rooms that are not perfect rectangles. By the end, you will be able to measure almost any space with confidence, and check your work against a free square footage calculator.

The basic square footage formula

For any rectangular room, square footage is length times width, both measured in feet. A room that is 10 feet long and 12 feet wide is 10 × 12 = 120 square feet. That is the entire formula for a simple rectangle, and it is the building block for every other calculation in this guide.

The trick is not the multiplication. It is measuring the right dimensions in the first place, and knowing what to do when a room is not a clean rectangle.

Converting square feet to square yards and square meters

Carpet and some turf products are priced by the square yard, not the square foot. To convert, divide your square footage by 9, since one square yard equals 9 square feet (a 3 ft by 3 ft square). A 900 square foot living room is 900 ÷ 9 = 100 square yards.

For metric jobs or international clients, multiply square feet by 0.09290304 to get square meters. This is the exact conversion factor confirmed by NIST's guide to the SI, and it is worth using the full number rather than rounding to 0.093, especially on larger commercial jobs where small rounding errors add up.

How to calculate square footage of a house

When you are measuring a whole house rather than a single room, the standard practice is to measure from the outside of the exterior walls, not the inside face of the drywall. This is the approach laid out in the ANSI Z765 standard that Fannie Mae and Freddie Mac require appraisers to follow, and it is also what most real estate listings use.

Measure the length and width of each floor separately, calculate the area of each, then add the floors together for total finished square footage. Basements typically are not counted under this standard, even when finished, so keep that separate from your interior square footage if you are quoting flooring or paint work down there. For quick, repeatable field measurements, a square footage calculator saves you from redoing the arithmetic by hand on every job.

Square footage formula for an L-shaped room

There is no single formula for an irregular room. Instead, you split it into two or more rectangles, calculate each one, and add the results. This works for L-shapes, U-shapes, and almost any floor plan a residential or light commercial job throws at you.

Say Dana is quoting new flooring for a basement rec room. The main body of the room is 14 feet by 12 feet, and a smaller extension juts out along one wall, 6 feet by 8 feet. Dana measures each rectangle separately, multiplies each one, and adds the two areas together for the true total.

On an earlier job, Dana only measured the main rectangle and missed the extension entirely. The flooring order came up 48 square feet short, which meant a second trip to the supplier and a delayed install. Breaking the room into rectangles first, on paper or in a takeoff tool, catches that kind of miss before the order goes out. If you are working from a full plan set rather than a tape measure, the same rectangle-by-rectangle approach is the basis of a proper construction takeoff.

Rooms with alcoves and closets

Closets, alcoves, and bump-outs are just smaller rectangles you add to or subtract from the main shape, depending on what the number is for. If you are ordering flooring for the whole room including the closet, measure the closet as its own small rectangle and add it to the total. If you only need the open floor area for furniture layout, you might leave the closet out on purpose. Decide what the number is for before you start measuring, because the same room can have two different correct answers.

Common mistakes that throw off your numbers

• Measuring the wrong wall face. Interior drywall-to-drywall measurements will always be smaller than exterior wall-to-wall measurements. Pick one method and stay consistent, and match the ANSI standard if the number is going on a listing or appraisal.
• Forgetting to subtract windows and doors for paint. Square footage for flooring is floor area, but square footage for a paint job is wall area, and wall area needs the window and door openings subtracted, or you will over-order paint.
• Skipping waste percentage on material orders. Flooring, tile, and roofing all get cut, trimmed, and occasionally damaged in shipping. Ordering the exact calculated square footage almost always leaves you short.
• Rounding too early. Round your final answer, not the individual measurements. Rounding each rectangle to the nearest foot before adding them up can shift a total by several square feet on a larger job.
• Mixing units mid-calculation. Convert everything to feet before you multiply. A common error is leaving one dimension in inches and multiplying it directly against a measurement in feet.

Square footage for flooring, paint, and price per square foot

For flooring, tile, and carpet, calculate the room's total area first, then add a waste allowance before you place the order. The National Wood Flooring Association's installation guidelines recommend a minimum 5% waste allowance for straight installations, rising toward 10% or more for rooms with angled walls, diagonal patterns, or a lot of cuts around cabinets and fixtures.

For paint, the number you want is wall area, not floor area. Measure the height and length of each wall, multiply, add the walls together, then subtract the area of windows and doors. Skipping that subtraction is one of the most common reasons a paint order comes up short on a room with a lot of glass.

Square footage also drives price per square foot, a shorthand contractors, appraisers, and clients all use to sanity-check a bid. Once you know a job's true square footage, whether from a tape measure on-site or a full plan takeoff like the one used to calculate cubic yards of concrete for a slab, dividing total cost by total square footage gives you a number you can compare against similar jobs.

Running these numbers by hand works fine for a single room. It gets tedious fast across a whole house, a commercial buildout, or a season's worth of estimates, which is exactly what a dedicated square footage calculator and a proper estimating workflow are built to speed up.

Frequently asked questions

How do you calculate square footage of a house?

Measure the length and width of each floor from the outside of the exterior walls, in feet, then multiply length by width for each floor and add the floors together. This outside-wall method matches the ANSI Z765 standard that most appraisers and real estate listings use, so your number will match what a buyer or lender expects to see.

How do you calculate square footage for flooring?

Measure the room in square feet using length times width (breaking it into rectangles if it is L-shaped), then add a waste percentage, usually 10% for a simple rectangular room and 15% or more for rooms with lots of cuts, angles, or diagonal layouts, before you order material.

What is the square footage formula for an L-shaped room?

Split the room into two or more rectangles, calculate the area of each one separately with length times width, then add the results together. There is no single formula for an irregular shape; you are just adding up simple rectangles.

How do I calculate square yards from square feet?

Divide the total square feet by 9. A 900 square foot room is 900 ÷ 9 = 100 square yards. This conversion comes up most often when pricing carpet, which is frequently sold by the square yard.

How do I convert square feet to square meters?

Multiply the square footage by 0.09290304, which is the exact conversion factor published by NIST. A 1,000 square foot space is 1,000 × 0.09290304, or about 92.9 square meters.