Square Footage Calculator
Enter dimensions and shape to calculate area in square feet. Supports rectangles, triangles, and circles with conversion to square meters and acres.
What is Square Footage?
A square footage calculator computes the area of a space in square feet based on its dimensions and shape. Square footage is the standard unit of area measurement in U.S. construction, real estate, and home improvement. Knowing the exact square footage is essential for estimating materials (flooring, paint, roofing), determining property values, sizing HVAC systems, and complying with building codes that regulate room sizes and window-to-floor area ratios. For rectangular spaces (the most common in construction), area is simply length multiplied by width. A 20-foot by 15-foot room equals 300 square feet. Most rooms, lots, and buildings are rectangular or can be broken into rectangular sections for calculation. When measuring irregular floor plans, divide the space into rectangles, calculate each section, and sum the results. Triangular areas appear in gable walls, roof sections, corner lots, and decorative landscape features. The area of a triangle equals one-half times the base times the height. The base and height must be perpendicular to each other — the height is measured straight up from the base, not along a sloped side. Circular areas apply to round rooms, columns, circular driveways, pools, and landscape features. The area of a circle equals pi (3.14159) times the radius squared. Since diameter is often easier to measure than radius, this calculator accepts the diameter as the length input and divides by two internally. The additional room field allows combining two spaces without switching between calculations. Enter the primary room dimensions normally, then add a previously calculated area (a closet, alcove, or second room) in the secondary field to get a combined total. For complex multi-room calculations, calculate each room separately and sum the primary areas. Square footage converts to other area units as follows: divide by 9 for square yards, multiply by 0.0929 for square meters, and divide by 43,560 for acres. One acre equals 43,560 square feet, roughly the size of a football field without end zones. These conversions are useful when working with international specifications (metric), ordering carpet (sold by square yard), or evaluating land parcels (acres). When measuring for construction, always measure from wall to wall at floor level. Include closets, alcoves, and bay windows in the room area. Do not include wall thickness (the space inside the wall cavity). For exterior measurements (roofing, siding), measure the outside face of the structure. Accuracy to the nearest half-foot is sufficient for most material estimates.
How to Calculate
- Measure the length of the space in feet (for circles, measure the diameter)
- Measure the width in feet (for circles, this field is ignored)
- Select the shape: rectangle, triangle, or circle
- Optionally enter an additional room area in square feet to combine spaces
- Review the primary area, total area, and unit conversions
- For irregular rooms, break into rectangles, calculate each, and add using the secondary field
Formula
Rectangle: Area = Length x Width Triangle: Area = 0.5 x Base (Length) x Height (Width) Circle: Area = π x (Diameter / 2)² Total Area = Primary Area + Secondary Area Square Meters = Total Area x 0.0929 Acres = Total Area / 43,560 Where π = 3.14159 and 43,560 is the number of square feet in one acre.
Example Calculation
A rectangular room 20 ft x 15 ft with no additional area: Shape = Rectangle Primary Area = 20 x 15 = 300 sq ft Secondary Area = 0 sq ft Total Area = 300 + 0 = 300 sq ft Total Area (sq m) = 300 x 0.0929 = 27.87 sq m Total Acres = 300 / 43,560 = 0.006887 acres
Frequently Asked Questions
How do I calculate square footage of an irregular room?
Break the room into rectangular sections, calculate each section's area (length x width), and add them together. For L-shaped rooms, divide into two rectangles. For rooms with angled walls, approximate with a rectangle plus a triangle. For very irregular shapes, use the triangulation method: divide into triangles from a central point and sum the triangle areas.
Is square footage measured from inside or outside walls?
It depends on the purpose. Interior livable square footage (for real estate listings and room sizing) is measured from the inside face of finished walls. Exterior square footage (for roofing, siding, or building footprint) is measured from the outside face of exterior walls. The difference is typically 5 to 10% due to wall thickness (4.5 to 6 inches per wall).
What is not included in livable square footage?
Standard real estate practice excludes: garages, unfinished basements, unfinished attics, covered porches and patios, crawl spaces, and any space with ceiling height below 7 feet. Finished basements are often listed separately. Stairways are counted once (on the level where you step onto them). Always check your local MLS guidelines for specific rules.
How many square feet is an acre?
One acre equals exactly 43,560 square feet. A square acre would be approximately 209 feet per side. For context, a standard football field (without end zones) is about 48,000 square feet or 1.1 acres. A typical suburban residential lot ranges from 5,000 to 15,000 square feet (0.11 to 0.34 acres).
How do I convert square feet to square meters?
Multiply square feet by 0.0929 to get square meters (or divide by 10.764). For example, 1,000 square feet equals 92.9 square meters. Going the other direction, multiply square meters by 10.764 to get square feet. One square meter equals approximately 10.76 square feet.