Square Footage Calculator

How to calculate square feet

This square foot calculator (also called a square footage calculator) finds the area of a rectangle, circle, or triangle from two measurements. For a rectangle, multiply length × width in feet. A 12 ft × 10 ft room is 12 × 10 = 120 sq ft. Circles use π × radius² and triangles use base × height ÷ 2.

You can measure in feet, inches, yards, or meters. The calculator converts everything to feet first, then reports the area in square feet, square yards, square meters, and acres. Add a price per square foot and it multiplies that out for a total cost.

Flooring, tile, paint, sod, carpet, roofing, and concrete are all estimated from square footage, so measure it carefully once and reuse it.

Square footage formulas by shape

Shape	What to enter	Formula
Rectangle / square	Length and width	Length × Width
Circle	Diameter (in the length field)	π × (Diameter ÷ 2)²
Triangle	Base (length) and height (width)	Base × Height ÷ 2

Rectangle or square. Rooms, patios, decks, garden beds, and driveways are usually rectangles. Multiply the two sides.

Circle. Measure straight across the widest point to get the diameter. The calculator halves it to get the radius, squares the radius, and multiplies by π (about 3.14159). Use this for round patios, fire-pit pads, tree rings, and above-ground pool footprints.

Triangle. The height must be measured at a right angle to the base, not along the slanted side. Half of base × height gives the area. Triangles show up in corner flower beds, angled lot lines, and gable ends of walls.

Converting units to square feet

If you measured in another unit, the calculator converts each side to feet before multiplying. These are the factors it uses:

You measured in	Each side is multiplied by	Area conversion
Inches	÷ 12	sq in ÷ 144 = sq ft
Feet	× 1	—
Yards	× 3	sq yd × 9 = sq ft
Meters	× 3.28084	m² × 10.764 = sq ft

A common error is converting only one side. A 120 in × 144 in floor is 17,280 sq in. Divide that by 144 (12 × 12), not 12, and you get 120 sq ft.

Worked examples

These match what the calculator above returns for the same inputs.

Example 1: a 12 × 10 ft bedroom (rectangle, feet).

• 12 × 10 = 120 sq ft
• 120 ÷ 9 = 13.33 sq yd
• 120 ÷ 10.7639 = 11.15 m²
• 120 ÷ 43,560 = 0.0028 acres

Example 2: a 10 ft round patio (circle, feet).

• Radius = 10 ÷ 2 = 5 ft
• 5 × 5 × 3.14159 = 78.54, shown as 79 sq ft
• 8.73 sq yd, 7.30 m²

Example 3: a room measured in meters, priced at $3.50/sq ft.

A room 4 m × 3.5 m:

• 4 × 3.28084 = 13.12 ft and 3.5 × 3.28084 = 11.48 ft
• 13.12 × 11.48 = 150.69, shown as 151 sq ft (14.00 m², 16.74 sq yd)
• 150.69 × $3.50 = $527 total

Example 4: a triangular corner bed, 20 ft base × 15 ft height.

• 20 × 15 ÷ 2 = 150 sq ft, or 16.67 sq yd

Square footage of common room sizes

Room size	Square feet	Square yards
10 × 10 ft	100 sq ft	11.11 sq yd
10 × 12 ft	120 sq ft	13.33 sq yd
12 × 12 ft	144 sq ft	16.00 sq yd
12 × 15 ft	180 sq ft	20.00 sq yd
14 × 16 ft	224 sq ft	24.89 sq yd
20 × 20 ft (two-car garage)	400 sq ft	44.44 sq yd

Area unit reference

Unit	Equals
1 square foot	144 sq in, 0.1111 sq yd, 0.0929 m²
1 square yard	9 sq ft
1 square meter	10.764 sq ft
1 acre	43,560 sq ft (about 208.7 ft × 208.7 ft)

How to measure an irregular area

Few spaces are perfect rectangles. Break the area into simple shapes, measure each one, and add them.

1. Sketch the space. Draw a rough outline on paper. It does not need to be to scale.
2. Divide it into shapes. Cut the outline into rectangles first, then use triangles and circles for the leftover angles and curves.
3. Measure each piece. Write each length and width on the sketch so nothing gets measured twice.
4. Calculate each piece. Run each shape through this square foot calculator.
5. Add the pieces together. Then subtract anything you will not cover.

L-shaped room example. A 15 × 12 ft main area plus an 8 × 6 ft nook is 180 + 48 = 228 sq ft. If a 4 × 6 ft kitchen island sits in the middle and won’t get new flooring, subtract 24 sq ft for 204 sq ft.

Yard with a curved end. A 30 × 20 ft rectangle with a half-circle on one 20 ft side: the rectangle is 600 sq ft, and a full 20 ft circle is 314.16 sq ft, so the half is 157.08 sq ft. Total: about 757 sq ft.

For walls, measure the width of each wall times the ceiling height, add them, and subtract doors (about 21 sq ft for a standard 3 × 7 ft door) and windows.

Common mistakes

• Mixing units. Feet on one side and inches on the other will give a wrong answer. Convert first, or measure both sides in the same unit and pick it from the dropdown.
• Writing 10’6“ as 10.6. Six inches is half a foot, so 10’6“ is 10.5 ft. Divide the inches by 12: 3“ = 0.25 ft, 9“ = 0.75 ft.
• Using radius in the diameter field. The circle option expects the full width across. Entering the radius gives an area one quarter of the true size.
• Measuring the slanted side of a triangle. Height must be perpendicular to the base.
• Forgetting waste. The calculator gives exact area. Most flooring and tile jobs need 5–10% extra for cuts, and diagonal or herringbone layouts often need 15% or more.
• Ignoring closets and alcoves. Measure them as separate rectangles and add them if they get the same material.

Common uses for square footage

Once you have the area, these calculators turn it into a shopping list:

• Flooring: the flooring calculator adds waste and converts to boxes. For carpet sold by the square yard, use the carpet calculator.
• Tile: the tile calculator converts square feet to tile count for any tile size.
• Paint: wall square footage goes into the paint calculator to get gallons.
• Lawn and sod: yard area goes into the sod calculator. Large lots are easier in acres with the acreage calculator.
• Mulch, soil, gravel, and concrete: add a depth and use the cubic yard calculator to find how much bulk material to order.
• Quick conversions: the square feet to square yards and square meters to square feet converters handle one-off unit changes.

Square feet vs. square yards vs. cubic yards

Square feet and square yards both measure flat area. A square yard is a 3 ft × 3 ft square, so it holds 9 sq ft. Carpet and some sod are priced per square yard. Flooring, paint coverage, and drywall are priced per square foot.

Cubic yards measure volume, so you also need a depth. A 120 sq ft bed covered 3 inches deep is 120 × 0.25 = 30 cubic feet, or 1.11 cubic yards. That is why soil, mulch, and gravel orders start with square footage and then add depth.

Accuracy note

The area is only as accurate as your tape measure. Round up when ordering, and confirm quantities and pricing with your supplier or installer before you buy.