Area & perimeter calculator
Choose a rectangle, circle, triangle, or trapezoid, adjust the dimensions, and see exactly how the area and perimeter come together.
Give your shape a size.
Use the same unit for every dimension. Changing the unit relabels the measurements; it does not convert them.
From dimensions to an answer
Composite shape area calculator
Break an irregular figure into rectangles, triangles, and circle parts. Add each piece, and subtract any hole or cut-out corner. The default L-shape is a 10 × 6 rectangle with a 4 × 3 corner removed.
48 units²
Area and perimeter formulas chart
Area is in square units and perimeter is in length units. Use the perpendicular height wherever h appears.
| Shape | Area | Perimeter |
|---|---|---|
| Square (side s) | A = s² | P = 4s |
| Rectangle | A = wh | P = 2(w + h) |
| Triangle | A = ½bh | P = a + b + c |
| Parallelogram | A = bh | P = 2(a + b) |
| Trapezoid | A = ½(a + b)h | Add all four sides |
| Rhombus | A = ½d₁d₂ | P = 4s |
| Circle | A = πr² | C = 2πr = πd |
| Semicircle | A = ½πr² | P = πr + 2r |
| Regular polygon | A = ½ × perimeter × apothem | P = ns |
Area and perimeter questions
Wondering about the why? Start here.
What is the difference between area and perimeter?
Area measures the space inside a flat shape and uses square units, such as cm². Perimeter measures the distance around its boundary and uses length units, such as cm. Shapes can have equal areas but different perimeters.
Compare area and perimeterHow do I calculate the area of a triangle?
Multiply the base by its perpendicular height, then divide by two: A = bh/2. A base of 8 cm and a height of 5 cm give 20 cm². The height must meet the base, or its extension, at a right angle.
Explore triangle areaCan I enter dimensions in different units?
Convert every length to the same unit before entering it. For example, 2 m and 50 cm become 2 m and 0.5 m, giving a rectangle area of 1 m². The calculator does not automatically convert mixed units.
Try the rectangle calculator