Square Footage Calculator: Rooms, L-Shapes and Circles

How to use this square footage calculator

Choose the unit you measured in: feet, inches, meters, or centimeters.
Pick a shape for each part of the space and enter its dimensions. Use Add shape for more parts.
Mark areas you will not cover, such as islands or built-ins, as Cut-out; they are subtracted.
Read the total in square feet, square meters, and square yards. Large areas also show acres.

How to calculate square footage: formulas for each shape

Square footage is area measured in square feet. Each shape has its own area formula; the calculator adds the shapes and subtracts the cut-outs.

Rectangle: length × width
Triangle: base × height ÷ 2 (height measured square to the base)
Circle: π × (diameter ÷ 2)²
Trapezoid: (side 1 + side 2) ÷ 2 × height, where sides 1 and 2 are the parallel sides

Measurements in inches, meters, or centimeters are converted to feet first. One square yard is 9 square feet and one acre is 43,560 square feet (NIST Handbook 44); one foot is exactly 0.3048 m.

Default example. An L-shaped room: a 20 × 12 ft rectangle plus an 8 × 6 ft alcove, minus a 3 × 4 ft area that won't be covered. Change the inputs above and the result panel recalculates; this worked example always shows the default.

Default example arithmetic

Shape 1     = 20 ft × 12 ft = 240 ft²
Shape 2     = 8 ft × 6 ft = 48 ft²
Cut-out     = 3 ft × 4 ft = 12 ft²
Total       = 240 + 48 − 12 = 276 ft²
Square yds  = 276 ÷ 9 = 30.667 yd²
Square m    = 276 × 0.3048² = 25.641 m²

Three shapes drawn at one scale in feet: shapes 1 and 2 are added together and shape 3 is a hatched cut-out that is subtracted — The default example's shapes drawn at one scale, with the cut-out hatched.

Square footage of common room sizes

Square footage of common rectangular room sizes, with square meters and square yards, computed with the same formula as the calculator.

Square footage of common room sizes
Room size	Square feet	Square meters	Square yards
10 × 10 ft	100	9.29	11.1
10 × 12 ft	120	11.1	13.3
12 × 12 ft	144	13.4	16
12 × 14 ft	168	15.6	18.7
14 × 16 ft	224	20.8	24.9
16 × 20 ft	320	29.7	35.6
20 × 20 ft	400	37.2	44.4
24 × 24 ft	576	53.5	64

Round areas: a circle 10 ft across is 78.5 sq ft, and 20 ft across is 314.2 sq ft.

Quick answers: square footage of common rooms and lots

Each answer is computed with the same formula as the calculator, using its default settings unless the question says otherwise.

How many square feet is a 12x15 room?

A 12 × 15 ft room is 180 square feet, which is 16.7 m² or 20 square yards.

How many square feet is a 16x24 garage?

A 16 × 24 ft garage is 384 square feet, which is 35.7 m² or 42.7 square yards.

How many square yards is a 12x18 room?

A 12 × 18 ft room is 24 square yards (216 sq ft).

How many acres is a 200x300 ft lot?

A 200 × 300 ft lot is 60,000 square feet, or 1.377 acres.

How many square feet is a 50x100 lot?

A 50 × 100 ft lot is 5,000 square feet, or 0.115 acres.

How many square feet is a 12 foot circle?

A circle 12 ft across is 113.1 square feet (10.5 m²), from π × radius².

How many square feet is a triangle with a 10 ft base and an 8 ft height?

A triangle with a 10 ft base and an 8 ft height is 40 square feet, half of base × height.

How many square feet is a 3x4 m room?

A 3 × 4 m room is 12 m², or 129.2 square feet.

How many square feet is 120x96 inches?

An area of 120 × 96 in is 80 square feet.

Using square footage to buy materials

Square footage is the starting point for most material orders. The default example totals 276 sq ft. Carry that number into the calculator for your material:

Floor tile and flooring: the tile calculator adds grout joints, waste, and box counts.
Wall paint: the paint calculator takes total wall area and the coverage on your paint label.
Drywall: the drywall calculator converts wall and ceiling area to sheets.
Mulch, gravel, or topsoil: multiply area by depth, or use the mulch, gravel, or topsoil calculator.

Most materials need an allowance for cuts and waste on top of the measured area. Those calculators apply it before rounding up.

Area calculator for L-shaped and irregular spaces

Most rooms and yards are not one rectangle. Split the space into shapes you can measure, enter each one, and mark any piece you are not covering (a kitchen island, a fireplace hearth, a pool) as a cut-out.

L-shaped rooms

Draw a line that splits the L into two rectangles. Measure each rectangle separately so no area is counted twice.

Curved beds and odd shapes

Approximate curves with several rectangles or trapezoids, or use the averaging methods in measuring irregular areas.

Tips for measuring square footage accurately

Measure to the nearest inch, then enter feet with decimals (6 in = 0.5 ft) or switch the unit to inches.
For floors, measure wall to wall inside the room. Include closets if they get the same flooring.
For a triangle, the height is measured at a right angle to the base, not along the sloped side.
Sketch the space and label each shape before you start. It makes double-counting easy to spot.
A laser distance measure is faster and more accurate than a tape for long rooms.

Square footage calculator FAQ

How do I calculate square footage?

For a rectangle, multiply length by width in feet. For other shapes, use their area formula: triangle = base × height ÷ 2, circle = π × radius². For a room made of several shapes, add the pieces together and subtract anything you won't cover.

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

Split the L into two rectangles, find each area, and add them. For example, a 20 × 12 ft area plus an 8 × 6 ft alcove is 240 + 48 = 288 sq ft. Subtracting a 3 × 4 ft area you won't cover gives 276 sq ft.

How many square feet are in a square yard?

Nine. A square yard is 3 ft × 3 ft. Divide square feet by 9 to get square yards.

How many square feet are in an acre?

An acre is 43,560 square feet, as defined in NIST Handbook 44. Divide square feet by 43,560 to get acres.

How do I convert square feet to square meters?

Multiply by 0.09290304. One foot is exactly 0.3048 meters, so one square foot is 0.3048 × 0.3048 = 0.09290304 square meters.

How do I measure square footage in inches?

Switch the unit to inches and enter the measurements as they are. The calculator converts to square feet; by hand, divide square inches by 144.

How do I find the area of a circle in square feet?

Measure the diameter across the widest point, halve it for the radius, and multiply π by the radius squared. A circle 10 ft across has an area of about 78.5 sq ft.

Should I include closets and hallways?

Include any area that will get the same material. For flooring, closets usually count; for a room's listed size, conventions vary, so follow whatever the measurement is for.

Calculators

Tile Calculator — Tiles and whole boxes for a floor or wall from the area, tile size, grout joint, waste allowance, and the count or coverage on the box.
Paint Calculator — Gallons or liters of paint for your walls and number of coats, using the coverage printed on your paint's label.
Drywall Calculator — Drywall sheet count for walls and ceilings from room dimensions or total area, minus openings, by sheet size.
Mulch Calculator — Mulch volume in cubic yards for any bed, plus a whole-bag count for the bag size you are buying.

Guides

How to Measure an Irregular Area — Split odd shapes into rectangles, triangles, circles, and trapezoids, then average width and depth.
Tile Layout Patterns and How They Change Your Order — Common tile patterns, the industry offset and grout joint rules for large tile, centering a layout, and overage by pattern.
What Is a Cubic Yard? — What a cubic yard is, how to convert area × depth into yards, and how much ground one yard covers.

Sources

NIST Handbook 44 (2026), Appendix C: Units of Area — National Institute of Standards and Technology. Used for: 1 yd² = 9 ft²; 1 acre = 43,560 ft²; 1 ft² = 144 in². Checked 2026-10-05.
NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity — National Institute of Standards and Technology. Used for: 1 ft = 0.3048 m (exact); 1 in = 2.54 cm (exact). Checked 2026-10-03.