Area Calculator – Rectangle, Circle & Triangle
Free area calculator: compute the area of rectangles, circles, and triangles from dimensions. Use for flooring, painting, landscaping, and geometry. No sign-up.
Area Calculator
Calculate area for rectangle, circle, or triangle. Enter dimensions in any unit (feet, meters, etc.); result is in square units.
How the area calculator works
Rectangle: area = length × width
Circle: area = π × radius²
Triangle: area = ½ × base × height
Use consistent units for all inputs. The result is in square units of that measure.
Understanding area and when to use this calculator
Area is the measure of a two-dimensional surface—how much space a shape covers. Whether you are laying flooring, ordering paint, planning a garden, or solving geometry problems, knowing the area is essential. This calculator handles the three most common shapes: rectangles (including squares), circles, and triangles.
For a rectangle, multiply length by width. A room 12 feet by 15 feet has an area of 180 square feet. For a circle, use π (approximately 3.14159) times the radius squared. A circle with a 5-foot radius has an area of about 78.5 square feet. For a triangle, use half the base times the height—the height is the perpendicular distance from the base to the opposite vertex.
Construction and home improvement projects often require area calculations. The tile calculator uses floor area to estimate how many tiles you need. The paint calculator uses wall area to estimate gallons of paint. The concrete calculator uses length, width, and depth to find volume, but area is the first step for slab projects. The roofing calculator estimates shingle coverage from roof area.
Use consistent units throughout. If you measure in feet, the area is in square feet. If you measure in meters, the area is in square meters. Our length converter can help you switch between units. For irregular shapes, divide the shape into rectangles, triangles, or circles, calculate each part, and add the results. This calculator runs in your browser and does not store your data.