Calculate the perimeter and area of rectangles, circles, triangles, polygons, and more. See the formula, step-by-step solution, and a labeled diagram.
Tap a shape to autofill an example.
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The perimeter is the total distance around the outside of a two-dimensional shape — the length you'd walk if you traced its edges. For straight-sided shapes like rectangles and triangles, you simply add up the side lengths; for round shapes like circles, the perimeter is called the circumference and uses π. This calculator finds the perimeter of ten common shapes — rectangle, square, triangle, circle, parallelogram, trapezoid, rhombus, regular polygon, ellipse, and circle sector — and also shows the area, the formula, a step-by-step solution, and a labeled diagram.
Perimeter is the total length of the boundary of a flat shape, measured in linear units such as feet, meters, or inches. It answers practical questions like how much fencing a yard needs, how much trim a room takes, or how long a running track is. Perimeter is different from area, which measures the space inside a shape (in square units). This calculator computes both at once: enter your shape's dimensions and it returns the perimeter and the area, along with the exact formula used and each step of the calculation.
Rectangle Formula
Check perimeter and area answers with full working shown.
Measure the perimeter of a lot to estimate how much fencing to buy.
Find the perimeter of a room or picture to buy the right amount of trim or molding.
Calculate edging for a garden bed of any shape.
Measure the boundary of a shape for binding, ribbon, or piping.
See how perimeter and area change across rectangles, circles, and polygons.
Rectangle, square, triangle, circle, parallelogram, trapezoid, rhombus, regular polygon, ellipse, and sector — no need to hunt for a separate calculator.
Most calculators give only one. This one shows both the perimeter and the area whenever the dimensions allow.
Every result comes with the formula and a step-by-step solution, so it's a study aid, not just an answer.
A clear diagram of your shape shows exactly which side each input refers to.
Work in inches, feet, yards, centimeters, meters, or millimeters — the perimeter and area carry your unit.
Add the length and width, then multiply by 2: P = 2 × (length + width). For example, a rectangle 5 feet long and 3 feet wide has a perimeter of 2 × (5 + 3) = 16 feet. Its area is length × width = 15 square feet.
It depends on the shape. A rectangle is 2(l + w), a square is 4s, a triangle is a + b + c, a circle (circumference) is 2πr, and a regular polygon is n × s (number of sides times side length). For any straight-sided shape, the perimeter is just the sum of all side lengths.
Add the lengths of all three sides: P = a + b + c. For example, a triangle with sides 3, 4, and 5 has a perimeter of 12. If you know all three sides, this calculator also finds the area using Heron's formula.
Yes. The distance around a circle is called its circumference, which is the circle's perimeter. It equals 2πr (or πd, where d is the diameter). For a circle with radius 7, the circumference is 2 × π × 7 ≈ 43.98 units.
Perimeter is the distance around the edge of a shape, measured in linear units (feet, meters). Area is the amount of space inside the shape, measured in square units (square feet, square meters). A 5×3 rectangle has a perimeter of 16 feet but an area of 15 square feet.
Multiply the number of sides by the length of one side: P = n × s. For example, a regular hexagon (6 sides) with each side 6 units long has a perimeter of 6 × 6 = 36 units. This works because all sides of a regular polygon are equal.