What shapes does the Area Calculator support?

Rectangle, square, circle, triangle, trapezoid, parallelogram and ellipse. Pick a shape from the segmented control and the input fields change to match it.

How does the area of a circle calculator work?

It applies the standard formula area = π × radius². Enter the radius (not the diameter) and the Area Calculator shows both the area and the circumference.

Can I use the Area Calculator for square footage of a room?

Yes. Choose Rectangle, enter the room's width and length in feet, and the area shown is in square feet — enter any consistent unit and the result is in that unit squared.

Why doesn't the triangle calculator show a perimeter?

The area of a triangle calculator here uses base and height, which is enough for area but not for the three side lengths needed to compute a perimeter, so only area is shown.

Is the ellipse circumference exact?

No exact elementary formula exists for an ellipse's circumference, so the Area Calculator uses Ramanujan's well-known approximation, which is accurate to within a fraction of a percent for most shapes.

Does the Area Calculator upload my measurements?

No. Every calculation runs locally in your browser. The dimensions you type never leave your device and nothing is sent to ArrayKit's servers.

Area Calculator Online

Calculate the area of circles, rectangles, triangles, trapezoids and more in your browser. Your numbers stay on your device.

The Area Calculator runs entirely in your browser. The dimensions you enter are computed locally and never leave your device.

Open the Volume Calculator

About Area Calculator

Area Calculator finds the area of seven common shapes — rectangle, square, circle, triangle, trapezoid, parallelogram and ellipse — from the dimensions you type in. Pick a shape, fill in its sides, base, height or radius, and the result updates instantly, along with the perimeter or circumference when it can be computed from what you entered. It is useful for flooring and paint estimates, garden or land measurements, classroom geometry homework, and any quick check of a shape's size before you order materials. Every formula is the standard textbook version, so results match what you would get by hand. Everything is computed locally in your browser as you type, with nothing uploaded.

Features

Covers seven shapes: rectangle, square, circle, triangle, trapezoid, parallelogram and ellipse
Switch shapes with one click and the input fields update automatically
Shows perimeter or circumference alongside area when it can be derived
Standard geometry formulas, including Ramanujan's ellipse circumference approximation
Copy a plain-text summary of the shape and its results in one click
Clear warning when a dimension is missing, zero, or negative
Updates the result live as you type — no calculate button needed
Runs entirely in your browser with nothing uploaded

How to use the Area Calculator

Choose a shape from the segmented control
Enter the required dimensions (e.g. width and height, or radius)
Read the computed area and, where shown, the perimeter or circumference
Copy the result summary or switch shapes to try another calculation

Example

Input

circle r=5

Output

Area: 78.54

Circle area uses π × radius²: π × 5² ≈ 78.54.

Common errors & troubleshooting

Area shows as 0 or the calculator won't produce a result. — Every visible field for the chosen shape needs a positive number — a blank, zero, or negative dimension is treated as incomplete.
No perimeter is shown for a triangle or trapezoid. — The Area Calculator only shows perimeter when it can compute it exactly from the given inputs (e.g. a rectangle's width and height); base/height alone isn't enough to find a triangle's side lengths.
The circle result looks off compared to a diameter measurement. — Enter the radius, not the diameter — the radius is half the diameter, and area of a circle calculator formulas expect radius in π × r².
Units don't match the expected square footage. — The Area Calculator is unit-agnostic — enter all dimensions in the same unit (e.g. feet) and read the result in that same squared unit.

Frequently asked questions

What shapes does the Area Calculator support?: Rectangle, square, circle, triangle, trapezoid, parallelogram and ellipse. Pick a shape from the segmented control and the input fields change to match it.
How does the area of a circle calculator work?: It applies the standard formula area = π × radius². Enter the radius (not the diameter) and the Area Calculator shows both the area and the circumference.
Can I use the Area Calculator for square footage of a room?: Yes. Choose Rectangle, enter the room's width and length in feet, and the area shown is in square feet — enter any consistent unit and the result is in that unit squared.
Why doesn't the triangle calculator show a perimeter?: The area of a triangle calculator here uses base and height, which is enough for area but not for the three side lengths needed to compute a perimeter, so only area is shown.
Is the ellipse circumference exact?: No exact elementary formula exists for an ellipse's circumference, so the Area Calculator uses Ramanujan's well-known approximation, which is accurate to within a fraction of a percent for most shapes.
Does the Area Calculator upload my measurements?: No. Every calculation runs locally in your browser. The dimensions you type never leave your device and nothing is sent to ArrayKit's servers.

Related tools

Surface Area Calculator — Calculate the surface area of spheres, cylinders, cones, boxes and more.
Volume Calculator — Calculate the volume of spheres, cylinders, cones, boxes and more.
Circle Calculator — Find a circle’s radius, diameter, circumference and area from any one value.
Triangle Calculator — Solve a triangle from sides and angles, with area, perimeter and type.
Right Triangle Calculator — Solve a right triangle from any two sides or a side and an angle.