Perimeter Calculator – Accurate, Instant & Ad-Free

Calculate the perimeter of any shape instantly with our Free Perimeter Calculator. Whether you’re a student solving geometry problems, a designer calculating boundaries, or an engineer working on real-world measurements, this tool gives you accurate results in seconds.

At Digital Calculator, we make geometry simple, visual, and reliable. Our Perimeter Calculator handles everything from basic 2D shapes like rectangles and circles to complex polygons and triangles. It automatically applies the correct formula and displays results in your preferred units centimeters, meters, inches, or feet.

No manual calculations or errors just instant, accurate perimeter results every time.

What Is the Perimeter?

The perimeter is the total length of the boundary of a two-dimensional shape. It represents the distance around the shape’s edges or the total measurement of its outline.

Think of it as the “fence length” needed to enclose a shape whether it’s a square garden, a circular pond, or a triangular plot.

Perimeter is always measured in linear units (cm, m, ft, in), unlike area or volume, which are measured in square or cubic units.

Perimeter Calculator: Supported Shapes

Our Free Perimeter Calculator can find the perimeter of:

Square
Rectangle
Triangle (equilateral, isosceles, scalene)
Circle (circumference)
Parallelogram
Trapezoid
Polygon (with any number of sides)

Each shape uses a specific formula that our calculator automatically applies based on your input.

Perimeter Formulas for Common Shapes

Let’s go through each shape’s perimeter formula, with simple examples to illustrate how our calculator computes the results.

Perimeter of a Square

Formula:
P = 4a

Where:

a = side length

Example:

a = 6 cm

P = 4 × 6 = 24 cm

Result: The perimeter of the square is 24 cm.

Perimeter of a Rectangle

Formula:
P = 2(l + w)

Where:

l = length
w = width

Example:

l = 10 cm, w = 4 cm

P = 2 × (10 + 4) = 2 × 14 = 28 cm

Result: 28 cm

Perimeter (Circumference) of a Circle

Formula:
P = 2πr or P = πd

Where:

r = radius
d = diameter

Example:

r = 7 cm

P = 2 × 3.1416 × 7 = 43.98 cm

Result: 43.98 cm

Perimeter of a Triangle

Equilateral Triangle

Formula:
P = 3a

Where:

a = side length

Example:

a = 5 cm

P = 3 × 5 = 15 cm

Result: 15 cm

Isosceles Triangle

Formula:
P = 2a + b

Where:

a = equal side
b = base

Example:

a = 6 cm, b = 8 cm

P = 2 × 6 + 8 = 20 cm

Result: 20 cm

Scalene Triangle

Formula:
P = a + b + c

Where:

a, b, c = side lengths

Example:

a = 4 cm, b = 5 cm, c = 7 cm

P = 4 + 5 + 7 = 16 cm

Result: 16 cm

Perimeter of a Parallelogram

Formula:
P = 2(a + b)

Where:

a = base
b = side

Example:

a = 9 cm, b = 5 cm

P = 2 × (9 + 5) = 2 × 14 = 28 cm

Result: 28 cm

Perimeter of a Trapezoid

Formula:

P = a + b + c + d

Where:

a, b, c, d = sides

Example:

a = 10 cm, b = 8 cm, c = 6 cm, d = 7 cm

P = 10 + 8 + 6 + 7 = 31 cm

Result: 31 cm

Perimeter of a Regular Polygon

Formula:
P = n × s

Where:

n = number of sides
s = side length

Example:

n = 5, s = 9 cm

P = 5 × 9 = 45 cm

Result: 45 cm

How to Use the Free Perimeter Calculator

Our Free Perimeter Calculator is built for precision and simplicity:

Select your shape (e.g., square, circle, triangle, etc.).
Enter the required values (side, radius, or other dimensions).
Click “Calculate.”
Instantly get the perimeter value in your chosen unit.

Try the Free Perimeter Calculator now on Digital Calculator fast, accurate, and ad-free.

Step-by-Step Examples

Let’s walk through a few practical cases

Example 1: Square

Side = 8 cm

P = 4a = 4 × 8 = 32 cm

Answer: 32 cm

Example 2: Rectangle

Length = 12 m, Width = 8 m

P = 2(l + w) = 2 × (12 + 8) = 40 m

Answer: 40 m

Example 3: Circle

Radius = 3.5 m

P = 2πr = 2 × 3.1416 × 3.5 = 21.99 m

Answer: 21.99 m

Example 4: Regular Hexagon

Number of sides = 6, side length = 5 cm

P = n × s = 6 × 5 = 30 cm

Answer: 30 cm

Perimeter Formula Summary Table

Shape	Formula	Example Input	Perimeter Result
Square	4a	a = 6 cm	24 cm
Rectangle	2(l + w)	10 × 4 cm	28 cm
Circle	2πr	r = 7 cm	43.98 cm
Equilateral Triangle	3a	a = 5 cm	15 cm
Parallelogram	2(a + b)	9, 5 cm	28 cm
Trapezoid	a + b + c + d	10, 8, 6, 7 cm	31 cm
Polygon	n × s	n = 5, s = 9 cm	45 cm

Understanding Perimeter in Real Life

Perimeter is used in countless real-world situations, from everyday tasks to advanced design calculations.

1. Construction & Architecture

Used to calculate boundary lengths for walls, floors, fences, and plots.

2. Interior Design

Helps determine the trim or edging needed around surfaces or materials.

3. Landscaping

Used to measure garden borders, walking paths, and fence lengths.

4. Education

Essential for geometry learning, problem-solving, and area-related concepts.

5. Sports & Engineering

Applied in designing tracks, playgrounds, and mechanical components.

Our Perimeter Calculator ensures all these calculations are fast, simple, and precise.

Common Mistakes to Avoid

When calculating perimeters manually, errors can easily occur. Here’s how to avoid them:

Mixing units — Always use the same unit (cm, m, ft, etc.) for all sides.
Missing sides — Ensure you include all edges for polygons and trapezoids.
Incorrect radius or diameter use — For circles, confirm whether you’re using r or d.
Forgetting π — Always use π ≈ 3.1416 when calculating circumference.
Rounding too early — Round only after completing all steps.