Area Calculator: Rectangle, Triangle, Circle & Trapezoid

Calculate the area of a rectangle, triangle, circle or trapezoid from its dimensions. Use one length unit for every dimension; results include square feet and square meters. This is a flat-shape calculator, not a material order or room-layout planner.

Read How to Calculate Area: Rectangle, Triangle, Circle and Trapezoid for worked examples, height and radius checks, and square-unit conversions.

Rectangle area calculator

Area = length x width. For Length 12, Width 10 and Length unit Feet (ft), the area is 120 ft², or approximately 11.148365 m². A square is a rectangle with equal length and width.

Triangle area calculator

Area = base x perpendicular height / 2. A base of 10 ft and a perpendicular height of 6 ft give 30 ft². The height must meet the base, or its extended line, at a right angle. A sloping side is not generally the height. This tool does not calculate triangle area from three side lengths.

Circle area calculator

Area = pi x radius x radius. A radius of 3 ft gives approximately 28.274334 ft². The radius is half the diameter. If the diameter is 6 ft, enter Radius 3, not 6. This mode calculates area, not circumference or the volume of a sphere.

Trapezoid area calculator

Area = (parallel base A + parallel base B) / 2 x perpendicular height. Bases of 8 ft and 12 ft with a perpendicular height of 5 ft give 50 ft². The two bases must be parallel; the height is the shortest distance between their lines. In US terminology this is a trapezoid; some other regions use the word trapezium.

Convert square units correctly

Length conversion factors must be squared when converting areas. One foot is 0.3048 meters, so one square foot is exactly 0.09290304 square meters. One square foot is also 144 square inches. Dividing a square-inch area by 12 would be incorrect; divide by 144.

Each dimension must be greater than zero and no more than 1,000,000 in the selected length unit. These are software input limits. Changing the shape or unit clears dimensions to prevent a radius, height or unit value from being silently reused for a different meaning.

Rooms, irregular outlines and material quantities

For an L-shaped outline, divide it into nonoverlapping rectangles or triangles and calculate each part separately. Add their areas and subtract only the cutouts you actually intend to exclude. This version calculates one shape at a time and does not remember or add previous results.

For practical room measurements, use our Square Footage Calculator. For purchasing flooring, paint or other products, use the relevant material calculator and the manufacturer's coverage information. Geometric area alone does not determine waste, pack counts or installation suitability.

Calculations happen locally in your browser. This calculator does not save or transmit dimensions. The hosting website may separately use analytics or other services under its privacy policy.