How to Calculate the Square Footage of a Room or House

To calculate square footage, measure the length and width in feet and multiply them. A room 12 feet by 15 feet is 12 × 15 = 180 square feet. For an L-shaped or irregular room, divide the floor into simple shapes, calculate each area, and add them together. If your measurements include inches, convert them to decimal feet first by dividing by 12.

The basic formula

How to measure a room

1. Measure wall to wall along the floor at the longest point in each direction. A 25-foot tape or a laser measure works best.
2. Write down feet and inches, rounding to the nearest half inch.
3. Sketch the room and note closets, bump-outs and alcoves separately.
4. Measure twice. Walls are rarely perfectly square, so if two measurements of the same wall differ, use the larger one for buying materials.

Working with feet and inches

Convert inches to decimal feet before multiplying:

The classic mistake is writing 12′ 6″ as 12.6. Since 6 inches is half a foot, it is 12.5. The feet and inches calculator handles mixed measurements, including fractions of an inch.

L-shaped and irregular rooms

Add rectangles

Split the room into rectangles that do not overlap, find each area and add.

Or subtract the missing piece

Measure the full bounding rectangle and subtract the cut-out. For the same room, the bounding box is 20 ft × 20 ft = 400 ft², and the missing corner is 10 ft × 8 ft = 80 ft², leaving 320 ft². Doing it both ways is a good check.

Other shapes

For angled walls or curved bays, see how to find the area of a triangle and how to find the area of a circle. The square footage calculator combines multiple shapes in one project.

Adding waste for flooring and tile

You always need more material than the floor area, to cover cuts, mistakes and pattern matching.

Always round up to whole boxes, and buy from the same production lot so colors match. The flooring calculator and tile calculator include waste and box counts.

Converting square footage

Carpet is often priced per square yard; the carpet calculator handles roll widths and seams. For metric plans, the square feet to square meters converter gives exact values. Notice that area conversions use squared factors: a yard is 3 feet, so a square yard is 9 square feet.

Square footage and project costs

Most flooring, roofing, painting and cleaning quotes are priced per square foot, so the area converts straight into a budget. At $4.50 per square foot for installed laminate, the 178-square-foot room above would cost about 196 ft² × $4.50 ≈ $882 including the 10% waste allowance. When comparing contractor quotes, check whether each one prices the measured floor area or the material ordered, since a 10% difference in the base can look like a better price when it is not.

Wall and ceiling area

Floor area is not the same as wall area. For painting or drywall, multiply the room’s perimeter by the wall height:

The 12.5 × 14.25 ft room with 8 ft ceilings has 2 × (12.5 + 14.25) × 8 = 428 ft² of wall before subtracting doors and windows. The ceiling equals the floor area. See how much paint do I need for the next step.

Measuring a whole house

For a home’s total square footage, the American National Standards Institute standard ANSI Z765 is the method most US appraisers and many builders follow. In outline:

• Measure the exterior dimensions of each finished level.
• Count only finished, heated, above-grade space in the main figure.
• Report basements and below-grade space separately, even if finished.
• Exclude garages, unheated porches and open areas such as two-story foyers on the upper level.
• Require a minimum ceiling height for finished space, with limited exceptions under beams and sloped ceilings.

Because builders, tax assessors and listing agents sometimes use different methods, the same house can have several “square footage” numbers. When the figure matters for a purchase or appraisal, ask which method was used.

Common mistakes

• Treating inches as tenths of a foot (12′ 6″ ≠ 12.6 ft).
• Mixing feet and inches in one multiplication.
• Counting overlaps twice when splitting a room into rectangles.
• Forgetting closets, which usually get the same flooring.
• Converting with linear factors, such as dividing square feet by 3 to get square yards.