Area & Perimeter Calculator
Calculate the area and perimeter of any shape — square, rectangle, triangle, circle, trapezium, parallelogram, ellipse, regular polygon. Free, in your browser.
Area and Perimeter Calculator
How to Use the Area & Perimeter Calculator
Choose a shape
Pick from squares, rectangles, triangles, circles, parallelograms, trapeziums, ellipses, and regular polygons.
Enter the dimensions
The input boxes change to match the shape — sides, radius, height, or whatever that shape needs. Type your measurements.
Read area and perimeter
Both appear instantly. For a circle, the perimeter is its circumference. The numbers come out in whatever units you entered.
Switch shapes freely
Change the shape any time to compare, or to handle a different part of a drawing — one tool covers them all.
Area and Perimeter, All in One Place
Two Questions, Many Shapes
Almost every practical geometry question comes down to one of two things: how much space is inside a shape (its area) or how far it is around the edge (its perimeter). Area tells you how much paint, turf, tiling, fabric, or land you need; perimeter tells you how much fencing, edging, framing, or trim. They are different questions with different formulas, and each shape has its own — the area of a rectangle is length times width, of a triangle is half base times height, of a circle is πr², and so on. Rather than making you hunt for the right formula, this calculator gathers the common shapes in one place: square, rectangle, triangle (from its three sides, using Heron's formula), circle, parallelogram, trapezium, ellipse, and any regular polygon. Pick the shape, enter the measurements it asks for, and get both the area and the perimeter at once, with no formula-lookup required.
A few of these shapes hide genuinely useful mathematics. A triangle's area from its three sides uses Heron's formula, a beautiful 2,000-year-old result that needs no height at all — handy when you can measure the sides of a plot but not its altitude. A regular polygon's area grows in a precise way with its number of sides, and as that number rises it creeps ever closer to the circle's πr², which is the sense in which a circle is a polygon with infinitely many sides. The ellipse's area is the elegant πab (the two semi-axes in place of a single radius), though its perimeter has no simple exact formula and is given here by an excellent approximation. Seeing these shapes side by side, computed consistently, builds an intuition for how area and perimeter scale — and why, for instance, doubling a shape's size quadruples its area but only doubles its perimeter.
"Area is how much fits inside; perimeter is how far around. Almost every fencing, flooring, or fabric question is really one of those two — for whatever shape you happen to have."
From Gardens to Floor Plans
The everyday uses are endless. Gardeners and landscapers calculate turf and edging for lawns and beds of every shape; builders and decorators work out flooring, paint, and skirting; dressmakers compute fabric; and anyone laying out a room, a plot, or a design is reaching for area and perimeter constantly. The mix of shapes matters because the real world is rarely a neat rectangle — a plot might be a trapezium, a window an ellipse, a tabletop a regular hexagon. Being able to switch shapes in one tool, without re-learning a formula each time, is what turns a maths exercise into a practical instrument. And because everything runs locally in your browser and accepts any units, it is an instant, private way to get the two numbers that most projects actually need, for the shape actually in front of you.
10 Facts About Area & Perimeter
Area is the space inside; perimeter is the distance around.
A rectangle's area is length × width; its perimeter is 2(l + w).
Heron's formula finds a triangle's area from its three sides — no height.
A circle's perimeter is its circumference, 2πr.
Doubling a shape's size quadruples its area but only doubles its perimeter.
A regular polygon approaches the circle as its sides increase.
An ellipse's area is πab — but its perimeter has no simple exact formula.
The circle encloses the most area for a given perimeter.
Area is in square units; perimeter in plain (linear) units.
This tool covers eight shapes with one shared, tested engine.
Frequently Asked Questions
- Area measures the space inside a shape (in square units) — what you need for paint, turf, or flooring. Perimeter measures the distance around the edge (in plain units) — what you need for fencing, edging, or framing. This calculator gives both at once for whichever shape you choose.
- Choose Triangle and enter the three side lengths. The calculator uses Heron's formula, which finds the area from the sides alone without needing the height — ideal when you can measure the edges of a plot but not its altitude. It also checks that the three sides can actually form a triangle.
- Square, rectangle, triangle, circle, parallelogram, trapezium, ellipse, and any regular polygon. Selecting a shape changes the input boxes to match what that shape needs, so you only ever enter the measurements that are relevant.
- Whatever units you enter. If you type measurements in metres, the area comes out in square metres and the perimeter in metres. The calculator is unit-agnostic — just keep all the inputs for one shape in the same units.
- From the number of sides and the side length, using the standard regular-polygon formula. As the number of sides increases, a regular polygon's area approaches that of a circle with the same perimeter — which is the sense in which a circle is a polygon with infinitely many tiny sides.
- Because, unlike the circle, an ellipse has no simple exact formula for its perimeter — it requires advanced mathematics. The calculator uses Ramanujan's well-known approximation, which is accurate to a tiny fraction of a percent for any normal ellipse, more than enough for practical work. The area, πab, is exact.
- Because area depends on two dimensions multiplied together, so scaling both by 2 multiplies the area by 2 × 2 = 4, while the perimeter (a single dimension summed) only doubles. You can see this directly: enter a shape, then enter one twice the size, and compare.
- Yes. The calculation runs in your browser — nothing is uploaded, stored, or logged — and it works offline once loaded.
- For 3D shapes — cubes, spheres, cylinders, cones and more — use the Volume & Surface Area Calculator, which is built on the same engine and works the same way: pick a solid, enter the dimensions, and get the volume and surface area.
- Completely free, with no account, sign-up, or limit. It runs entirely in your browser and collects no data. Use it as often as you like.
Related News
You may be interested in these recent stories from our newsroom.
No related news yet for this tool. Our editorial team publishes new pieces every week.
Browse all news →75 more free tools
Calculators, converters, security tools — no signup.