Perimeter Calculator
Calculate perimeters for various shapes quickly and accurately
Perimeter Calculator – Free Online Perimeter Tool
The Perimeter Calculator helps you compute the perimeter (total boundary length) of common 2D shapes instantly. Whether you're a student solving geometry homework, a teacher preparing lessons, a DIY enthusiast planning materials, or a professional doing quick checks, this free online tool gives accurate results in seconds. No downloads, no signup — just enter the measurements and get the perimeter.
What is Perimeter?
Perimeter is the total distance around the edge of a two-dimensional shape. For simple polygons it is the sum of the side lengths. For curved shapes such as circles, perimeter is often called the circumference. Perimeter is measured in linear units such as mm, cm, m, inches, or feet.
Shapes Supported by This Perimeter Calculator
- Square (side × 4)
- Rectangle (2 × (length + width))
- Triangle (sum of three sides)
- Circle / Circumference (2 × π × r)
- Parallelogram (2 × (base + side))
- Trapezoid (sum of all four sides)
- Regular polygons (n × side length)
How to Use the Perimeter Calculator
- Select the shape you want to calculate the perimeter for (square, rectangle, triangle, circle, etc.).
- Enter the required measurements (side length, radius, base and height, or individual sides as needed).
- Choose the measurement units (cm, m, inches, feet, etc.) if the tool supports unit conversion.
- Click the Calculate button to see the perimeter instantly displayed.
- If needed, change units or re-enter values to recalculate.
Perimeter Formulas (Quick Reference)
- Square: P = 4 × a (where a = side length)
- Rectangle: P = 2 × (l + w) (l = length, w = width)
- Triangle: P = a + b + c (sum of all three sides)
- Circle (Circumference): C = 2 × π × r (r = radius) or C = π × d (d = diameter)
- Parallelogram: P = 2 × (base + side)
- Trapezoid: P = a + b + c + d (sum of all four sides)
- Regular n-sided polygon: P = n × s (n = number of sides, s = side length)
Examples
Example 1: Square with side 5 cm → P = 4 × 5 = 20 cm.
Example 2: Rectangle 8 m × 3 m → P = 2 × (8 + 3) = 22 m.
Example 3: Circle with radius 7 in → C = 2 × π × 7 ≈ 43.98 in.
When Should You Use a Perimeter Calculator?
The perimeter calculator is useful for many practical tasks: estimating fence length for a garden, measuring baseboard material for a room, planning trims for craft projects, computing border length for landscaping, and helping students verify homework answers. It’s also helpful in CAD or design checks where quick perimeter values are needed.
Unit Conversion Tips
If you input measurements in different units, convert them to the same unit before calculating. For example, convert inches to feet or cm to meters, depending on the desired output. Some tools offer built-in unit selection so results are displayed in your chosen unit automatically.
Frequently Asked Questions (FAQs)
1. What is the difference between perimeter and area?
Perimeter measures the length around a shape (one-dimensional), while area measures the surface inside a shape (two-dimensional). Perimeter is in linear units (like meters), area is in square units (like square meters).
2. Does this calculator handle circles?
Yes — for circles we compute the circumference using C = 2 × π × r. You can enter radius or diameter depending on the tool options.
3. Can I calculate the perimeter of an irregular polygon?
Yes. For irregular polygons, add the lengths of all edges to get the perimeter. If you have coordinates, some advanced tools compute distances between points and sum them up.
4. Why is the perimeter different when I change units?
Perimeter value depends on units. Converting the input dimensions to a different unit before calculation will change the numeric value but not the physical length — e.g., 100 cm = 1 m (so numeric values change according to unit conversion).
5. Is the Perimeter Calculator free to use?
Yes, this Perimeter Calculator is free, requires no signup, and works directly in your browser.
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Final Thoughts
The Perimeter Calculator is a small but powerful helper for students, professionals, and DIY enthusiasts. It eliminates manual arithmetic errors and speeds up planning tasks. Use it to estimate material requirements, verify homework answers, or quickly get perimeter values for any common shape.