Perimeter Calculator
Compute the perimeter of rectangles, squares, triangles, circles and irregular polygons. Choose the shape, enter side lengths and get the total boundary length plus conversions.
Calculator
Results
Perimeter in selected unit, plus automatic conversions.
Perimeter (selected unit)
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m
Perimeter (meters)
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Perimeter (centimeters)
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Perimeter (feet)
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Common perimeter formulas
| Shape | Formula | Notes |
|---|---|---|
| Square | P = 4a | a = side |
| Rectangle | P = 2(L + W) | L = length, W = width |
| Triangle | P = a + b + c | Any triangle, any sides |
| Circle | C = 2πr = πd | r = radius, d = diameter |
| Regular n-gon | P = n × s | n = number of sides, s = side length |
| Irregular polygon | P = Σ si | Sum all sides |
How this perimeter calculator works
Perimeter is the total distance around a 2D shape. Most shapes have very simple perimeter formulas, so the real challenge is supporting many shapes and many units in a single tool — exactly what this calculator does.
Supported shapes
- Rectangle: \( P = 2(L + W) \)
- Square: \( P = 4a \)
- Triangle: \( P = a + b + c \)
- Circle (circumference): \( C = 2 \pi r \)
- Regular polygon: \( P = n \times s \)
- Irregular polygon: sum of all side lengths
Units and conversions
You can enter your dimensions in mm, cm, m or inches. The calculator converts everything internally to meters so that it can output:
- perimeter in your selected unit (for example “3.5 m”)
- perimeter in meters
- perimeter in centimeters
- perimeter in feet (useful for construction or landscaping)
FAQ
How do I find the perimeter of a room?
Measure each wall and sum the lengths. If the room is rectangular, use 2 × (length + width). If it has odd corners, use the “Irregular polygon” option and list all sides.
What if I only know the area?
Perimeter cannot be uniquely determined from area alone, unless you know the shape (e.g. square). For mixed or unknown shapes you must measure the sides.
Why is circle included in a perimeter calculator?
Because the circumference is the perimeter of a circle, and it is one of the most common perimeter problems.
Formula (LaTeX) + variables + units
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- No variables provided in audit spec.
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - FTC — Consumer advice — consumer.ftc.gov · Accessed 2026-01-19
https://consumer.ftc.gov/
Last code update: 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.