Geometry
Area and perimeter calculator
Calculate the area and perimeter of common shapes. Choose a shape, enter its measurements and see the formula step by step.
Shape and measurements
Use the same unit for every measurement of the shape.
Result
Enter the measurements
The area, perimeter and formula will appear here.
- Area
- Pending
- Perimeter
- Pending
- Detail
Practical use
Use area for surfaces and perimeter for boundaries.
Show calculation
Formula: Select a shape and enter its measurements.
Substitution: The values will appear here.
Result: Complete the fields to calculate.
Formulas by shape
The calculator uses these formulas and keeps full precision throughout the calculation.
| Shape | Area | Perimeter |
|---|---|---|
| Square | side² | 4 × side |
| Rectangle | base × height | 2 × (base + height) |
| Triangle from three sides | √(s × (s - a) × (s - b) × (s - c)) | a + b + c |
| Triangle from base and height | (base × height) ÷ 2 | All three sides are required |
| Circle | π × radius² | 2 × π × radius |
| Regular polygon | (perimeter × apothem) ÷ 2 | number of sides × side length |
Linear and square units
Perimeter keeps the length unit. Area uses the same unit squared.
If you enter meters, the perimeter is shown in `m` and the area in `m²`. With no unit selected, area is shown as `units²`.
Area or perimeter
Choosing the right measurement avoids confusing estimates.
Use area for surfaces such as flooring, paint, fabric or land. Use perimeter for fences, edges, frames, baseboards or any boundary.
Also useful
Pythagorean theorem calculator
If you are working with right triangles, calculate the hypotenuse or a leg before using the area or perimeter.
Frequently asked questions
What is the difference between area and perimeter?
Area measures the surface a shape covers. Perimeter measures the length of its boundary.
When should I use area and when should I use perimeter?
Use area for covering surfaces such as flooring, paint or land. Use perimeter for edging, fencing, framing or measuring boundaries.
How do I calculate the area of a rectangle?
Multiply the base by the height. For example, a 5 m by 3 m rectangle has an area of 15 m².
How do I calculate the perimeter of a rectangle?
Add the base and height, then multiply by 2. For example, with a 5 m base and 3 m height: 2 × (5 + 3) = 16 m.
How do I calculate the area of a triangle?
If you know the base and height, multiply them and divide by 2. If you know all three sides, use Heron’s formula.
How do I calculate the area of a circle?
Multiply π by the radius squared. If you have the diameter, first divide it by 2 to get the radius.
Is circumference the perimeter of a circle?
Yes. A circle’s boundary length is called its circumference and is calculated as 2 × π × radius.
What units are used for area?
Area is expressed in square units such as cm², m² or ft². Perimeter is expressed in linear units such as cm, m or ft.
What does it mean for a polygon to be regular?
A regular polygon has sides of equal length and angles of equal measure.