ToolkitBook
Calculate the area of any 2D geometric shape instantly. Select from ten shapes including circles, ellipses, squares, rectangles, triangles, and trapezoids. Enter radius, side lengths, diagonals, or base and height depending on the shape. The tool displays area, perimeter, diagonals, and the formula used for each calculation. Architects determine floor areas from blueprints, landscapers calculate lawn square footage, students verify homework answers, and contractors estimate materials. Enter any unit consistently—results appear in corresponding square units. All processing runs locally in your browser.
Click the shape button that matches your measurement scenario. The interface shows ten options: circles, ellipses, squares, rectangles, rhombus, trapezoids, regular polygons, right triangles, equilateral triangles, and general triangles. When you select a shape, a diagram appears showing which dimensions you need to enter, and the formula displays above the input fields.
Each shape requires specific measurements. For circles, enter the radius—the distance from center to edge. If you measured diameter instead, divide by two first. For rectangles and squares, enter side lengths. For triangles, you can enter base and height, or for right triangles, the two legs forming the 90-degree angle. Trapezoids need both parallel side lengths plus the perpendicular height between them. Rhombus calculations use the two diagonals measured corner to corner through the center. Regular polygons need the number of sides and the side length.
Enter all dimensions in the same unit—meters, feet, inches, or centimeters. The calculator preserves your unit choice throughout: enter feet, get square feet in the result. Mixed units require manual conversion before entry. For a room measuring 3 meters by 200 centimeters, convert to 3 by 2 meters or 300 by 200 centimeters first.
The primary result shows area in large text. Below this, additional measurements appear based on shape type. Circles display circumference and diameter. Rectangles and squares show perimeter and diagonal length. Triangles show perimeter and, where applicable, height or hypotenuse. These secondary measurements help with material planning—perimeter for border materials, diagonals for fitting objects into corners, height for vertical clearance.
Flooring projects: Calculate room area to determine material quantity. Add 10% extra for waste and cuts. For irregular rooms, divide the space into rectangles, calculate each separately, then sum the results.
Landscaping: Measure lawn or garden bed area to order correct amounts of seed, fertilizer, soil, or mulch. For curved or irregular shapes, approximate with combinations of circles, rectangles, or triangles.
Paint and materials: Wall area calculations determine paint requirements. Ceiling area affects lighting plans. When measuring walls, subtract window and door areas for accurate paint estimates.
Property and construction: Lot sizes appear in real estate listings. Floor area ratios determine building limits. Contractors use area calculations for material estimates and project bids.
Verify measurements before entry. Common errors include confusing radius with diameter, or measuring along slanted sides instead of perpendicular height. For trapezoids, height must be measured at a right angle to the parallel sides, not along the angled edges. For circles, ensure you have the radius (center to edge), not the diameter (edge to edge through center). Use a tape measure or laser distance tool for accuracy.
Real rooms and objects rarely match perfect geometric shapes. A room might have slightly non-parallel walls. For such cases, take measurements at multiple points and use averages, or divide irregular spaces into simpler shapes that the calculator can handle individually.
Circle: A = π × r² (r = radius)Ellipse: A = π × a × b (a, b = semi-axes)Square: A = s² (s = side length)Rectangle: A = length × widthRhombus: A = (d₁ × d₂) / 2 (d₁, d₂ = diagonals)Trapezoid: A = (a + b) × h / 2 (a, b = parallel sides, h = height)Regular Polygon: A = (n × s² × cot(π/n)) / 4 (n = sides, s = side length)Right Triangle: A = (a × b) / 2 (a, b = legs)Equilateral Triangle: A = (√3/4) × s² (s = side length)General Triangle: A = (base × height) / 2