Square Footage Calculator

About the Square Footage Calculator

A square footage calculator computes the area of any space — rooms, lots, buildings, garden beds, or any flat surface — in square feet and optionally square metres. Knowing exact square footage is essential for purchasing the right amount of flooring, carpet, tile, or hardwood (including the proper waste allowance); calculating paint quantity for walls and ceilings; determining material costs for construction projects; listing property dimensions in real estate; sizing HVAC equipment; and solving a wide range of home improvement calculations. Our free square footage calculator handles all common shapes: rectangles and squares, triangles, circles and partial circles, L-shaped and T-shaped rooms, trapezoids, and irregular polygons. It includes a combined-area feature for whole-home square footage calculations and a room-by-room breakdown. Results display in square feet, square yards (for carpet purchasing), square metres, and acres for large properties.

How It Works

Rectangle or square: Area = Length x Width. A 13 ft x 17 ft bedroom = 221 sq ft. Triangle: Area = 0.5 x base x height. Circle: Area = π x radius². L-shaped room: divide into two rectangles, calculate each, add them. Example: an L-shaped room where the main area is 15 ft x 20 ft (300 sq ft) plus a 8 ft x 10 ft alcove (80 sq ft) = 380 sq ft total. For flooring: add a waste factor of 10% for straight installation, 15% for diagonal installation, 20% for herringbone or stone patterns. Paint coverage: 1 gallon covers approximately 350-400 sq ft. Wall area = (room perimeter x ceiling height) minus the area of all doors and windows. HVAC rule of thumb: 20-25 BTU per square foot for air conditioning in moderate US climates.

Tips & Best Practices

• ✓Flooring waste allowance: 10% for straight-lay tile and hardwood, 15% for diagonal, 20% for herringbone or complex stone patterns. Always buy extra from the same lot for future repairs.
• ✓Paint calculation: measure wall square footage as perimeter x height, subtract 21 sq ft per door and 15 sq ft per window. One gallon covers 350-400 sq ft, so divide by 375 for a typical estimate and round up.
• ✓Real estate definition: "finished square footage" in the US typically excludes unfinished basements, garages, and covered but unheated outdoor spaces. Methods vary by state and appraiser.
• ✓Carpet purchasing: carpet is sold by the square yard (not square foot). Divide your square footage by 9 to get square yards. Add 10% waste and account for roll width (typically 12 feet) to minimise seams.
• ✓Irregular rooms: photograph the room and sketch it with dimensions, then decompose it into rectangles and triangles. Measure each dimension independently — do not assume rooms are perfectly rectangular.
• ✓Lawn fertiliser and seed: sold per 1,000 sq ft on the label. Divide your lawn square footage by 1,000 to determine the number of bags needed at the recommended application rate.
• ✓Solar panel sizing: a typical 400W residential solar panel occupies approximately 17-20 sq ft. Roof area and shading determine the maximum system size before calculating the number of panels.
• ✓Property lot size: legal descriptions often give lot dimensions in feet. Calculate the square footage, then divide by 43,560 to convert to acres. 1 acre = 43,560 sq ft exactly.

Who Uses This Calculator

Homeowners purchasing flooring, tile, carpet, or paint for renovation projects. Real estate agents calculating and verifying listed property square footage. Landscapers and gardeners calculating bed and lawn areas for material ordering. Contractors preparing material estimates for construction bids. Property managers calculating commercial space rent per square foot.