How to calculate square footage
Square footage is simply length × width in feet. A room or lot 40 ft by 30 ft is 40 × 30 = 1,200 square feet. The calculator also converts that to square yards (÷ 9) and acres (÷ 43,560) for landscaping and real estate. Carpet and some flooring are sold by the yard, which the square yard calculator converts to.
How to use this calculator
Enter the length and width in feet. For an L-shaped or irregular area, break it into rectangles, find each one's square footage, and add them together. Round up when ordering materials.
Where square footage is used
Square footage drives flooring, paint, and material estimates, and it's the basis for real-estate pricing per square foot — see the price per square foot calculator. For depth-based materials like gravel or concrete, combine the area with a depth using the square feet to cubic yards calculator.
Record every dimension at floor level before you start multiplying, because walls are rarely perfectly square. Treat a triangular corner or a bay as half of its length times its width and add it to the rectangles. When measuring for materials, take the longest and widest points so you never come up short; when measuring for a listing or a lease, follow whatever measurement standard the agreement names, since those rules decide whether stairs, closets and unfinished space count at all. For a room you are refitting, take the area straight into the flooring calculator.
Frequently asked questions
- How do I calculate square footage?
- Multiply length by width in feet. A 40 ft by 30 ft area is 1,200 square feet.
- How many square feet are in an acre?
- 43,560 square feet make one acre.
- How do I find square footage of an irregular room?
- Split it into rectangles, calculate each rectangle's square footage, and add them together.
- How do I convert square feet to square yards?
- Divide by 9. 1,200 square feet is about 133.3 square yards.
- Do I measure to the inside or outside of the walls?
- Measure inside face to inside face for flooring, paint and tiling. Real-estate and roofing figures usually use the exterior footprint, so the same room can honestly return two different numbers.