Square Footage Calculator
Calculate the area of any space in square feet — rectangles, circles, and triangles.
Reviewed by the ToolNestr Editorial Team — July 2026
How the square footage calculator works
The calculator computes the area of three common shapes — rectangle, circle, and triangle — based on the dimensions you enter. For rectangles, it multiplies length by width. For circles, it uses pi times the radius squared. For triangles, it multiplies base by height and divides by two. The result is displayed in square feet and also converted to acres for larger areas.
To use the tool, select the shape that matches the space you are measuring. Enter the required dimensions in feet. The area updates automatically as you type. If you need to measure a room with multiple sections, calculate each section separately and add the totals together.
Square footage is the standard unit for real estate listings in the United States and Canada. It determines property value, renovation costs, material quantities, and even furniture fit. Knowing the exact area of each room helps you make informed decisions about flooring, paint, heating and cooling capacity, and spatial planning.
Living area (gross living area, or GLA) measurement conventions follow ANSI Z765-2021, the American National Standard for Determining Gross Living Area, used by appraisers and real estate professionals nationwide.
Measure dimensions
Use a tape measure to find the length, width, radius, or base and height of the space.
Select shape
Choose rectangle, circle, or triangle and enter your measurements in the input fields.
Read the result
The tool shows square footage and acres instantly. Use the total to plan materials or compare spaces.
The formula explained
Each geometric shape has a specific formula for calculating area. Understanding these formulas helps you verify measurements and adapt to unusual spaces:
Rectangle area
Area = L × W. A room that is 15 feet long and 12 feet wide has an area of 15 × 12 = 180 sq ft. This is the most common calculation in real estate and covers most rooms, hallways, and lots.
Circle area
Area = πr². A circular patio with a radius of 6 feet has an area of π × 6² = π × 36 ≈ 113.1 sq ft. Use this for round tables, circular rooms, or garden features.
Triangle area
Area = ½ × b × h. A triangular garden bed with a base of 8 feet and a height of 5 feet has an area of 0.5 × 8 × 5 = 20 sq ft. Triangles are common in angled lots and A-frame structures.
Worked example
A living room measures 18′ × 14′ with a rectangular bay window area of 6′ × 3′ attached.
Use cases for the square footage calculator
Home buyer or seller
Compare the square footage of homes you are considering. Verify listed dimensions against your own measurements. Accurate square footage directly affects property valuation and listing price.
Renovation planning
Estimate flooring, paint, and tile quantities for each room. Knowing the exact square footage helps you buy the right amount of materials without costly waste or shortages.
Contractor bidding
Provide accurate area measurements in client proposals. Square footage drives pricing for flooring installation, painting, drywall, and many other trades.
Landscaping
Measure lawn areas for sod, garden beds for mulch, and patios for pavers. The circle and triangle modes handle curved beds and angled corners that rectangles miss.
Tips for measuring square footage
Measure from wall to wall
Always measure between the interior wall surfaces, not including baseboards or trim. For exterior measurements, measure from the outside of the walls. Real estate listings typically use interior dimensions for living area and exterior dimensions for the total building footprint.
Break complex rooms into sections
An L-shaped room is simply two rectangles added together. A room with a bay window is a rectangle plus a smaller rectangle or triangle. A circular turret is a circle. By combining shapes, you can measure any floor plan accurately with just a tape measure and this calculator.
Account for obstructions
Permanent fixtures like built-in cabinets, fireplaces, and columns reduce usable square footage. Measure around them or subtract their area from the room total. For renovation material estimates, measure the full floor area since materials must go around these features.
Round to the nearest half foot
Perfect precision is rarely necessary for most projects. Measuring to the nearest half foot (6 inches) gives sufficient accuracy for flooring, paint, and tile estimates. For critical cuts, measure to the nearest inch and double-check before cutting.
Real-world context
Appraisers use this exact rectangle-plus-circle-plus-triangle decomposition when calculating gross living area for a listing. Consider an L-shaped ranch home: a main block measuring 22 ft by 16 ft (352 sq ft) plus an attached wing measuring 10 ft by 8 ft (80 sq ft) totals 432 sq ft, or about 0.0099 acres — a figure that would need to be added to every other room in the house to reach the total GLA reported on a listing sheet.
Circular features come up more often than people expect — round patios, gazebos, and turret-style rooms all use the pi-r-squared formula. An 8 ft radius circular patio works out to π × 8² ≈ 201.1 sq ft, or roughly 0.0046 acres, which is enough space for a standard patio table, four chairs, and a small grill with room to walk around.
Triangle mode is most useful for angled lots and gable-end walls. A triangular side yard with a 45 ft base and a 30 ft height (measured perpendicular to the base) covers 0.5 × 45 × 30 = 675 sq ft, about 0.0155 acres — a common shape where a rectangular lot meets a curved street or property line at an angle.
Common misconceptions
"Square footage on a listing always matches what you'd measure yourself." Not necessarily. Different appraisers and county assessors sometimes use different conventions — some include finished basements or garages, others exclude them entirely per ANSI Z765 guidelines. Always verify by measuring the living area yourself if square footage is critical to your decision.
"A bigger radius circle takes proportionally more material than a bigger rectangle." Circles scale differently. Because circle area depends on the radius squared, doubling a circular patio's radius quadruples its area (not doubles it) — a detail that catches people off guard when budgeting pavers or concrete for a larger round feature.
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Frequently asked questions
What is the difference between square footage and square feet?
They mean the same thing. Square footage is the area measured in square feet. Both terms are used interchangeably in real estate and construction.
How do I measure an irregularly shaped room?
Break it into rectangles, triangles, and circles. Calculate each separately using this tool and add the results together.
Is the garage included in square footage?
In most US real estate listings, garages are not counted in the living area square footage (GLA). They are listed separately.
What about stairs and hallways?
Stairs are counted once per floor. Measure the length and width of the stairwell opening or the tread area. Hallways are measured as rectangles.
Sources & references
This tool uses standard formulas and reference values from:
- • American Concrete Institute — ACI 318, Building Code Requirements for Structural Concrete. concrete.org
- • ICC — International Residential Code (IRC), span, footing and framing tables. codes.iccsafe.org
- • APA – The Engineered Wood Association, allowable span and load guidance.
Estimates for planning only. Span, load and code values vary by jurisdiction — verify against your local adopted code and a licensed engineer before building.