Area and Perimeter Calculator
Pick a 2D shape, type its measurements and get the area and the perimeter (or circumference) at once. The calculator covers ten shapes, from squares and circles to scalene triangles by Heron’s formula, trapezoids, regular polygons and circle sectors, and it shows which formula was used with your numbers substituted in.
Find the Area and Perimeter of a Shape
Result
Formula and working
How to Use the Area and Perimeter
- Choose the shape; only the measurements it needs are shown.
- Pick a unit (optional) and enter the lengths.
- Press Calculate to see the area, perimeter and extra values such as diagonals or arc length.
About This Tool
Students learning mensuration, DIY-ers measuring floors, gardens or fabric, and tradespeople estimating materials such as paint, turf or edging.
Input: Lengths · Output: Area and perimeter.
Features and Limitations
Features
- Ten shapes, including Heron’s formula for any triangle from its three sides.
- Checks impossible input, such as sides that cannot form a triangle or a height longer than a slanted side.
- Extra results: diagonals, apothem, interior angle, arc length and triangle height.
- Area units are squared automatically (cm → cm²).
Limitations
- The ellipse perimeter is Ramanujan’s approximation (extremely close, but not exact, because no simple exact formula exists).
- Irregular polygons and composite shapes need to be split into simpler shapes first.
- All measurements must use the same unit; there is no mixed-unit conversion.
- Results are computed in your browser; nothing you enter is sent to a server.
Example
Rectangle 8 × 5 cm: area 40 cm², perimeter 26 cm. Circle with radius 3: area ≈ 28.27433388, circumference ≈ 18.84955592. Triangle 3-4-5: s = 6, area = √(6 × 3 × 2 × 1) = 6.
Frequently Asked Questions
How do I find the area of a triangle when I only know the sides?
Use Heron’s formula: s = (a + b + c) ÷ 2, then area = √(s(s − a)(s − b)(s − c)). Choose “Triangle (three sides)” and the calculator does this for you.
What is the difference between perimeter and circumference?
Both are the distance around a shape; circumference is the name used for circles.
Why does a trapezoid need its legs?
The area only needs the two parallel sides and the height, but the perimeter also needs the lengths of the two slanted legs.
Which unit is the area in?
The square of the length unit you chose: centimetres give cm², feet give ft². With “No unit” it is reported in square units.
Related Tools
More like this: all Math tools, all Calculators tools or the TinySandy home page.