How do I find the square footage of an L-shaped room?

Measure the overall rectangle the room fits in, then subtract the missing corner rectangle. A 30 × 20 ft outline with a 12 × 10 ft notch is 600 − 120 = 480 sq ft.

How many square meters is a square foot?

Exactly 0.09290304 m², because one foot is defined as exactly 0.3048 m. To go from square meters to square feet, divide by 0.09290304 (about 10.764 sq ft per m²).

Why is my total smaller than the listed square footage of my house?

Listings usually follow ANSI Z765, which measures finished living area from the exterior walls and includes wall thickness, hallways and stairs. Adding up interior room dimensions leaves those out, so it typically comes in 10–15% lower.

How much extra flooring should I buy?

Add about 5–10% to the square footage for straight installations and 10–15% for diagonal or patterned layouts to cover cuts and mistakes.

Square Footage Calculator

Add up the square footage of rooms and areas of any shape (rectangles, L-shapes, triangles, trapezoids and circles) in feet and inches or meters, with an optional cost estimate.

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How to measure a room for square footage

Measure wall to wall at floor level with a tape or laser measure, and write down feet and inches separately. Convert the inches to a decimal by dividing by 12: 12 ft 6 in is 12.5 ft, and 10 ft 9 in is 10.75 ft. Multiply length by width for each rectangular space, then add the spaces together. A 20 × 15 ft living room (300 sq ft), a 12 × 12 ft bedroom (144 sq ft) and a 12 × 10 ft kitchen (120 sq ft) total 564 sq ft, which is 52.40 m².

Round each measurement to the nearest inch, not the nearest foot. Rounding a 12 ft 5 in wall down to 12 ft on both sides of a 12 × 12 room understates it by almost 10 sq ft, and the error compounds across a whole house.

Odd-shaped rooms: L-shapes, triangles, trapezoids and circles

L-shape: measure the full rectangle the L fits inside, then subtract the missing corner. A 30 × 20 ft area with a 12 × 10 ft cut-out is 600 − 120 = 480 sq ft. This is easier and less error-prone than splitting the L into two rectangles.
Triangle (angled bay or corner nook): ½ × base × height, where height is measured at a right angle to the base.
Trapezoid (a room with one angled wall): ½ × (side A + side B) × height. Sides of 10 and 14 ft that are 8 ft apart give 96 sq ft.
Circle (round sunroom or patio): π × (diameter ÷ 2)². A 10 ft circle is about 78.5 sq ft.

For anything more complex, break the space into these shapes and add them up as separate areas.

What counts toward a home's listed square footage

Measuring for flooring or paint is not the same as measuring a home for sale. Appraisers and many listing services follow ANSI Z765, which reports finished, heated, above-grade living area measured from the exterior walls. Under that standard, garages, unfinished basements, and areas with ceilings under 7 ft are not counted, and below-grade finished space is reported separately. Sums of interior room sizes will usually come in 10–15% below the listed figure because they leave out wall thickness, hallways, closets and stairwells.

Use interior room totals for materials such as flooring, carpet and paint. For pricing a home, compare like with like: listing square footage against listing square footage.

Turning square footage into a cost estimate

Enter a price per square foot to get a total. Flooring is priced this way: at $4.50 per sq ft, the 564 sq ft example costs about $2,538 before installation. Add 5–10% for waste on straight lays and 10–15% for diagonal or herringbone patterns, because cut pieces at the walls can't all be reused.

The calculator also shows square yards (carpet is often sold by the yard: divide square feet by 9) and acres (divide by 43,560), and converts to square meters using the exact factor 1 sq ft = 0.09290304 m².

Frequently Asked Questions

Common questions about the Square Footage Calculator

Multiply the length by the width of each rectangular room in feet, then add the rooms together. For a 12 × 15 ft room that is 180 sq ft. Convert inches to feet first by dividing by 12.