Square Footage Calculator
Square footage is one of the most frequently needed calculations in home improvement, real estate, flooring, painting, and landscaping. This square footage calculator handles five common shapes and includes an add-to-total feature so you can calculate multiple rooms or areas and see a running total. For rectangles, enter length and width. For triangles, enter the base and the perpendicular height. For circles, enter the diameter. For trapezoids (a four-sided shape with two parallel sides), enter both parallel sides and the perpendicular height. For L-shaped rooms, either use the L-shape option (entering the outer length, outer width, and the notch dimensions) or calculate two rectangles and add them. All dimensions are in feet. The calculator also shows the area in square yards (divide by 9) and square metres (divide by 10.764), which are useful for some material pricing. Areas can be added individually to build a total project area. This is useful when measuring flooring for a whole house, calculating paint for multiple rooms, or estimating mulch for multiple garden beds. Click the Add to total button after each calculation to accumulate rooms, then use the grand total for your material order.
Area formulas
Rectangle: A = Length x Width
Triangle: A = 0.5 x Base x Height
Circle: A = pi x (Diameter / 2)^2
Trapezoid: A = 0.5 x (Side1 + Side2) x Height
L-shape: A = (Outer L x Outer W) - (Notch L x Notch W)
Square footage calculator: frequently asked questions
How do I calculate square footage of a room?
For a rectangular room, multiply the length by the width in feet. For example, a 14 x 12 ft room = 168 square feet. For L-shaped rooms, break the space into two rectangles, calculate each area, and add them together. For rooms with angled walls, break the space into rectangles and triangles and sum the areas.
How do I calculate square footage of a circle?
Area of a circle = pi x radius^2. Enter the diameter of the circle and the calculator divides by 2 to get the radius. For example, a 20 ft diameter circular patio: radius = 10 ft. Area = pi x 10^2 = 314.16 sq ft.
How do I calculate square footage of a triangle?
Area of a triangle = 0.5 x base x height. For a right triangle with a 10 ft base and 8 ft height: area = 0.5 x 10 x 8 = 40 sq ft. The height must be perpendicular to the base. For an irregular triangle, use Heron's formula if you know all three sides, but for most practical purposes measuring the base and perpendicular height is easiest.
What is the square footage of a trapezoid?
Area of a trapezoid = 0.5 x (Base 1 + Base 2) x Height. The two bases are the parallel sides and the height is the perpendicular distance between them. For a trapezoidal room with parallel walls of 10 ft and 14 ft and a depth of 8 ft: area = 0.5 x (10 + 14) x 8 = 96 sq ft.
How many square feet are in an acre?
One acre equals exactly 43,560 square feet. One square mile equals 640 acres or 27,878,400 square feet. For real estate and land measurement, the chain and link system historically defined an acre as 10 square chains (66 ft x 660 ft). For practical lot and plot measurements, most assessors and surveyors now use square feet directly.
Sources
- NIST Handbook 44, Units of Measurement: nist.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General reference only; verify measurements on site.