Square Footage Calculator

To find square footage, change any inches to feet and multiply length by width: a room 15 ft 6 in by 12 ft is 15.5 × 12 = 186 sq ft. This square footage calculator also handles triangles, circles, trapezoids and borders, adds L-shaped sections, subtracts cutouts, and turns the total into square meters, square yards, acres, flooring boxes and cost.

How to use the square footage calculator

1. Choose Feet + inches or Meters + cm at the top.
2. For each area, pick a shape and type its measurements. You can fill feet, inches or both, so 15 ft 6 in needs no conversion.
3. Split an L-shaped or irregular room into simple shapes with + Add area. Use − Add cutout for a closet, kitchen island or hearth you will not cover.
4. Use Count for identical areas, such as three bedrooms of the same size.
5. Open Flooring and cost to add a waste allowance, the coverage printed on one box and your price per square foot, square yard, square meter or box.

Each row draws its own diagram from your numbers, so a typo such as 51 ft instead of 15 ft shows up at a glance. Press Show steps to see every multiplication and conversion.

Square footage formulas for each shape

Area is always measured in square units. If every length is in feet, the answer is in square feet; if every length is in meters, the answer is in square meters.

The triangle height is measured straight up from the base at a right angle, not along a sloping side. For a trapezoid, a and b are the two parallel sides.

Measuring in feet and inches

A tape measure gives feet and inches, but the formulas need one unit. Divide the inches by 12 and add them to the feet: 10 ft 9 in = 10 + 9 ÷ 12 = 10.75 ft. Writing 10 ft 9 in as 10.9 ft is a common slip that makes a 10 ft 9 in by 12 ft room come out 1.8 sq ft too big. The calculator takes feet and inches in separate boxes so you never have to do this by hand.

Measure each wall at floor level, wall to wall, and round up to the next half inch. If a room is not quite square, measure both opposite walls and use the longer one.

Worked example: an L-shaped room

An L-shaped room measures 20 ft by 16 ft overall, with an 8 ft by 6 ft corner missing. There are two ways to get its area, and both should agree.

• Split it: one rectangle 20 ft by 10 ft (200 sq ft) plus one 12 ft by 6 ft (72 sq ft) gives 272 sq ft.
• Subtract the notch: the full 20 × 16 = 320 sq ft rectangle minus the 8 × 6 = 48 sq ft corner also gives 272 sq ft.

In the calculator, the first method is two areas; the second is one area plus one cutout. Getting the same total both ways is a quick check on your measurements.

Worked example: flooring boxes and cost

A bedroom is 12 ft 9 in by 10 ft 6 in. The laminate you like covers 23.4 sq ft per box and costs $2.89 per square foot.

1. Convert: 12 ft 9 in = 12.75 ft and 10 ft 6 in = 10.5 ft.
2. Area: 12.75 × 10.5 = 133.875 sq ft, about 133.88 sq ft.
3. Add 10% waste: 133.875 × 1.1 ≈ 147.26 sq ft.
4. Boxes: 147.26 ÷ 23.4 ≈ 6.29, so buy 7 boxes. Always round up, because stores sell whole boxes.
5. Cost: 7 boxes hold 7 × 23.4 = 163.8 sq ft, and 163.8 × $2.89 ≈ $473.38.

Notice that the bill is based on the whole boxes, not on 147.26 sq ft. The calculator shows both numbers so you can see what rounding up costs.

Worked example: a round patio with a paver ring

A round patio is 12 ft across: π × 12² ÷ 4 ≈ 113.1 sq ft. If only a 2 ft wide ring of pavers runs around the edge, the inner circle is 12 − 2 × 2 = 8 ft across, and the ring covers π × (12² − 8²) ÷ 4 = π × 80 ÷ 4 ≈ 62.83 sq ft. Choose Ring in the calculator and type 12 ft and 8 ft.

Square feet conversion table

One foot is exactly 0.3048 m, so 1 sq ft = 0.3048² = 0.09290304 m² exactly. A square yard is 3 ft by 3 ft, so it holds 9 sq ft, and an acre is 43,560 sq ft. Going the other way, 1 m² ≈ 10.764 sq ft.

Carpet is often priced per square yard. To compare it with a per-square-foot price, divide the yard price by 9: $27 per sq yd is $3 per sq ft.

How much extra flooring to buy

Every floor needs some extra for cuts at walls, pattern matching and a few spare pieces for later repairs. A straight layout in a simple rectangular room needs the least. Diagonal layouts, herringbone, many corners and large tiles need more. Your flooring maker’s installation guide is the final word, so check it before you order, and keep unopened spare boxes with the receipt in case they can be returned.

Common square footage mistakes

• Treating inches as decimals. 6 inches is 0.5 ft, not 0.6 ft.
• Adding instead of multiplying. Length + width + length + width is the perimeter (for baseboard), not the area.
• Dividing by 3 for square yards. A square yard is 9 sq ft, so divide square feet by 9.
• Using the radius as the diameter. The circle formula here uses the full width across. If you know the radius, double it first.
• Forgetting closets or counting islands. Add closets you will floor and subtract fixed cabinets or islands you will not.
• Rounding boxes down. 6.29 boxes means 7 boxes.

Working on a geometry assignment rather than a floor? The area and perimeter calculator focuses on the math of each shape, including perimeter.

Square footage practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How do I calculate the square footage of a room?

Measure the length and width in feet, change any inches to feet by dividing by 12, and multiply. A 12 ft 6 in by 10 ft room is 12.5 × 10 = 125 sq ft. For odd shapes, split the room into rectangles and add their areas.

How many square feet is a 12 by 12 room?

A 12 ft by 12 ft room is 12 × 12 = 144 sq ft, which is 16 sq yd or about 13.38 m².

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

Split the L into two rectangles, find each area and add them. Or take the full rectangle around the L and subtract the missing corner. Both give the same answer, as in the 272 sq ft example above.

How do I convert square feet to square meters or square yards?

Multiply square feet by 0.09290304 to get square meters, and divide by 9 to get square yards. For acres, divide by 43,560.

How many boxes of flooring do I need?

Add your waste allowance to the room's area, divide by the square feet each box covers, and round up to a whole box. For 147.26 sq ft and boxes of 23.4 sq ft, that is 7 boxes.

Related calculators

• Area and perimeter calculator for geometry practice with every shape
• Concrete calculator for slabs, footings and bag counts
• Volume calculator for cubic feet and cubic yards
• Circle calculator for radius, diameter and circumference
• Pythagorean theorem calculator to check that a room's corners are square
• Unit converter for lengths and areas in other units

Sources

• NIST: U.S. survey foot, revised unit conversion factors (international foot = 0.3048 m exactly; acre = 43,560 sq ft), checked November 2026
• NIST Handbook 44, Appendix C: General tables of units of measurement (1 sq ft = 0.09290304 m²; 1 sq yd = 9 sq ft), checked November 2026