Perimeter Calculator
Calculate the perimeter of common geometric shapes including triangles, rectangles, squares, and circles. Get accurate measurements for any 2D shape instantly.
Result
- Shape
- -
- Perimeter
- -
Formula & Guide
Formulas
P
Rectangle
P = 2 × (L + W)
Add length and width, multiply by 2
P
Square
P = 4 × s
Multiply side length by 4
P
Triangle
P = a + b + c
Add all three side lengths
C
Circle (Circumference)
C = 2 × π × r
Multiply 2, π, and radius
Formula Variables
P
Perimeter
The total distance around the outside of a 2D shape
L, W
Length, Width
The dimensions of a rectangle
s
Side
The side length of a square (all sides equal)
a, b, c
Sides
The three side lengths of a triangle
r
Radius
The distance from center to edge of a circle
Step-by-Step Scenario
Example Scenario
Length
8 units
Width
5 units
1
Identify the Values
- Length = 8 units, Width = 5 units
Make sure all measurements use the same units
2
Apply the Formula
- Perimeter = 2 × (Length + Width)
- Perimeter = 2 × (8 + 5)
- Perimeter = 2 × 13
Additional Examples
Square
Side: 6 units
Perimeter
4 × 6 = 24 units
Triangle
Sides: 3, 4, 5 units
Perimeter
3 + 4 + 5 = 12 units
Characteristics of Perimeter
Linear Measurement
Perimeter is a linear measurement (one dimension), while area is a square measurement (two dimensions).
Additive Property
For polygons, perimeter is found by simply adding all side lengths. This makes it straightforward to calculate.
Practical Uses
Used for fencing, framing, borders, trim work, and any application where you need to know the distance around a shape.
Circle Special Case
For circles, the perimeter is called circumference and uses π in the formula, making it different from polygon perimeters.
Important Notes
- Perimeter is always expressed in linear units (e.g., meters, feet, inches) based on the units of the input measurements.
- For rectangles and squares, opposite sides are equal, which is why we multiply by 2 in the formula.
- Circle perimeter (circumference) uses π, which is approximately 3.14159, making it an irrational number.
- All measurements must use the same units. Mixing units (e.g., meters and feet) will give incorrect results.
- For irregular polygons, you would need to manually add all side lengths, which this calculator doesn't support.
Frequently Asked Questions
Find answers to common questions about perimeter calculations.