Square Footage Calculator
A square footage calculator finds the area of a room, yard, or building surface in square feet based on its shape and dimensions. Select rectangle, circle, or triangle, enter the measurements in feet, and the tool returns the total area instantly along with the exact formula it used. Contractors, flooring installers, painters, and homeowners use square footage figures to price materials, quote labor, and compare a listed room size against what a tape measure actually shows on site. A bedroom, a circular patio, and a triangular gable end each need a different formula, so this calculator switches the math automatically based on the shape selected instead of forcing every surface into one rectangle formula. Most real rooms are not a single perfect shape. For a floor plan with an alcove, a bay window, or an angled wall, split the space into two or more of the supported shapes, calculate each one with this square footage calculator, and add the results together to get the true total.
Quick answer
The result shows the total area of your surface in square feet (ft²).
What this tells you
- •The result shows the total area of your surface in square feet (ft²).
- •All inputs must be entered in feet. Convert inches to feet by dividing by 12 first.
- •For irregular shapes, calculate each section separately using the shape that fits it best, then add the areas together.
- •The secondary result shows the exact formula and numbers used, which is handy for double-checking the math by hand.
- •A circle's radius is the distance from the center to the edge, not the full width, or diameter, of the circle.
- •A triangle's height is the perpendicular distance from the base to the opposite point, not the length of a slanted side.
- •Square footage measures floor or surface area only. It does not include material waste, so add a waste percentage before ordering flooring, tile, or turf.
How to Use
- 1Select the shape that best matches your surface: rectangle, circle, or triangle.
- 2For a rectangle, enter the length and width in feet.
- 3For a circle, enter the radius in feet, measured from the center point to the edge, which is half the diameter.
- 4For a triangle, enter the base and the perpendicular height in feet, not the length of a slanted side.
- 5Click Calculate to see the total square footage along with the formula the tool used.
- 6For a room built from more than one shape, repeat the calculation for each section and add the results together, or use the Reset button to clear the fields and start over.
How It Works
Formula
Rectangle: Area = Length × Width
Circle: Area = π × Radius²
Triangle: Area = (Base × Height) ÷ 2All three formulas assume every measurement is already in feet, so the result comes out directly in square feet (ft²). For a rectangle, Length and Width are the two straight sides of the surface. For a circle, Radius is the distance from the center point to the edge, exactly half the diameter, and the calculator squares that value and multiplies it by π (approximately 3.14159). For a triangle, Height is the perpendicular distance from the Base to the opposite vertex, measured at a right angle to the base, not the length of either slanted side. Dividing the Base times Height product by 2 accounts for the triangle covering only half of the rectangle that would contain it. The calculator rounds the final area to two decimal places, and it also returns the exact numbers it used so the math can be checked by hand.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Rectangular bedroom
A bedroom measuring 14 feet by 12 feet has an area of 14 × 12 = 168.00 square feet. This is the number a flooring or carpet installer needs before writing a quote, and it is close to the figure most real estate listings use for that individual room.
Circular patio
A circular patio with an 8-foot radius covers π × 8² ≈ 201.06 square feet. Radius is half the width of the circle, not the full width, so entering the diameter by mistake would roughly quadruple the area.
Triangular garden bed
A triangular garden bed with a 10-foot base and a 7-foot perpendicular height covers (10 × 7) ÷ 2 = 35.00 square feet. Only the height measured straight up from the base counts. A tape measure run along the sloped edge of the bed would give a different, incorrect number.
One-car garage floor
A garage floor measuring 24 feet by 22 feet covers 24 × 22 = 528.00 square feet. That total is the starting point for an epoxy coating or concrete sealant estimate, before adding a waste allowance for cutting around the garage door track or a floor drain.
Round pool deck
A circular deck built around a pool with a 12-foot radius covers π × 12² ≈ 452.39 square feet. Decking material is usually priced by the board or by the square foot, so this figure is the starting point before adding waste for angled cuts along the curve.
L-shaped living room, split into two rectangles
An L-shaped living room does not fit a single rectangle formula, so split it into a main section and an alcove. The main section is 18 × 14 = 252.00 square feet, the alcove is 8 × 6 = 48.00 square feet, and adding them gives 300.00 square feet total. This split-and-add method works for any room built from rectangles, circles, or triangles.
Trapezoid deck, split into a rectangle and a triangle
Dana's deck is 10 ft deep, 22 ft along the house, and 16 ft along the outer edge, so it is a trapezoid. She runs it as two shapes: a 16 by 10 ft rectangle gives 160.00 sq ft, and the leftover triangle with a 6 ft base and a 10 ft perpendicular height gives (6 × 10) ÷ 2 = 30.00 sq ft. The total is 190.00 sq ft. Multiplying by the exact factor 0.09290304 gives 17.65 sq m, which is the figure her composite decking supplier quotes in.
Square footage by shape, with square meters
Worked areas for each shape the calculator offers, plus two common composites built from more than one run. The last column converts with the exact factor 1 sq ft = 0.09290304 sq m.
| Shape | Dimensions (ft) | Formula | Area (sq ft) | Area (sq m) |
|---|---|---|---|---|
| Rectangle | 12 x 10 | 12 x 10 | 120.00 | 11.15 |
| Rectangle | 15 x 12 | 15 x 12 | 180.00 | 16.72 |
| Rectangle | 20 x 14 | 20 x 14 | 280.00 | 26.01 |
| Circle | radius 5 | π x 5² | 78.54 | 7.30 |
| Circle | radius 8 | π x 8² | 201.06 | 18.68 |
| Circle | radius 10 | π x 10² | 314.16 | 29.19 |
| Triangle | base 10, height 7 | (10 x 7) ÷ 2 | 35.00 | 3.25 |
| Triangle | base 12, height 8 | (12 x 8) ÷ 2 | 48.00 | 4.46 |
| Triangle | base 16, height 9 | (16 x 9) ÷ 2 | 72.00 | 6.69 |
| Trapezoid (two runs) | rectangle 16 x 10 plus triangle base 6, height 10 | 160.00 + 30.00 | 190.00 | 17.65 |
| Border (two runs) | outer 20 x 16 minus inner 16 x 12 | 320.00 - 192.00 | 128.00 | 11.89 |
Square feet computed with the formulas above and rounded to two decimals as the tool does. Square meters use the exact factor 0.09290304 from NIST SP 811 Appendix B.8 and NIST Handbook 44 Appendix C, applied to the rounded square footage.
How to measure a room that is not a perfect rectangle
Most floor plans are not a single clean rectangle, circle, or triangle. A bedroom with a closet nook, an open living and dining area, or a patio with a curved edge is usually a combination of two or more basic shapes joined together.
Sketch the space on paper first and draw a line where one shape ends and the next begins. A living room with a rectangular main area and a bay window alcove becomes two rectangles. A patio with a straight edge on one side and a curved edge on the other becomes a rectangle plus part of a circle.
Measure and calculate each section separately with this calculator, matching the shape option to that section. Write down each result, then add them together for the total square footage of the whole space. Subtract any area that will not be covered, such as a fireplace hearth or a support column, if the project only needs the usable surface.
This same split-and-add approach works for uncommon layouts including L-shaped rooms, wraparound decks, and yards with a curved planting bed along one edge. Break the shape down until each piece matches a rectangle, circle, or triangle, and the math stays simple even when the room is not.
A home's listed square footage follows a different rulebook than a flooring takeoff. ANSI Z765-2021, Square Footage: Method for Calculating, published by Home Innovation Research Labs, is the residential measurement standard Fannie Mae and Freddie Mac reference. It counts finished, above-grade living area measured from the outside of the exterior walls, requires a ceiling height of at least 7 ft for the area to count, and applies to single-unit houses only, not 2 to 4 unit buildings or apartment-style condominiums. This calculator measures the surface you give it, usually the inside of a room, so it will come in below a Z765 figure for the same house because wall thickness is excluded. For the metric conversion, NIST SP 811 Appendix B.8 and NIST Handbook 44 Appendix C both define 1 sq ft as exactly 0.09290304 sq m, which is where the rounded 10.764 sq ft per square meter in the FAQ comes from.
Common mistakes
- Entering the diameter instead of the radius for a circle. The radius is half the diameter, so this mistake roughly quadruples the calculated area.
- Measuring the slanted side of a triangle instead of the perpendicular height from the base to the opposite point.
- Mixing units within one calculation. Every value must be in feet before calculating, so a measurement taken in inches or yards needs to be converted first.
- Forgetting to convert inches to feet. Divide the inch measurement by 12 before entering it.
- Treating an irregular floor plan as one shape instead of splitting it into rectangles, circles, and triangles and adding the results.
- Using outside wall measurements instead of the finished interior floor space, which overstates the usable area for flooring or paint estimates.
- Assuming the displayed square footage already includes material waste. Add a waste percentage on top of the calculated area before ordering flooring, tile, turf, or paint.
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