Perimeter Calculator
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Calculation Results
Perimeter:
Perimeter Calculator
Distance Around Any Polygon
Every polygon has a perimeter, the full distance around its outer edge. This calculator adds the sides for you across squares, rectangles, and triangles. Fence builders, seamstresses, and students use it for borders and trim.
Summing the Sides
Perimeter is the sum of all sides: P = a + b + c for a triangle and 2 x (Width + Length) for a rectangle. A square needs only its Side value, multiplied by four.
Example: a rectangle with Length 7 and Width 4 gives 2 x (7 + 4) = 22 units. A triangle with Side a 6, Side b 8, and Side c 10 totals 6 + 8 + 10 = 24 units.
A fencing job shows how a correct sum prevents ordering mistakes. A rectangular yard 30 ft long and 20 ft wide has 2 x (30 + 20) = 100 ft of run; choose Rectangle under the Perimeter of menu, enter Length 30 and Width 20, and 100 ft appears in the result. Fence panels sold in 8 ft sections divide 100 by 8, so buy 13 panels and plan one cut. Laying the addition out by hand as 30 + 20 + 30 + 20 reaches 100 too, but the tool catches any side you forgot.
Getting Correct Results
Open the Perimeter of menu, choose your shape, and fill in Width, Length, Side, or Side a, Side b, Side c as prompted. Press Calculate Perimeter to read the total.
Use one unit throughout; the Metric toggle only labels the output. Convert mixed units first, and make sure no side is left out of the sum.
Frequently Asked Questions
What is a simple perimeter example?
A square with Side 6 has a perimeter of 24 because 4 x 6 = 24. A 7 by 4 rectangle works out to 2 x (7 + 4) = 22.
Does it handle irregular triangles?
Yes. Enter Side a, Side b, and Side c with any valid lengths, and the perimeter is simply their sum, whatever the angles may be.
What is the triangle inequality rule?
Any two sides must add to more than the third, or no triangle can exist. Sides 2, 3, and 10 are impossible to join. The calculator cannot return a shape.
Are perimeter and area different?
Yes. Perimeter measures distance around a shape in units, while area measures the surface inside in square units. A 4 by 4 square has both equal to 16, coincidentally.
Are decimal side lengths allowed?
Decimals are welcome, so Side 6.5 or Width 3.25 works fine. Just keep every measurement in the same unit before pressing Calculate Perimeter. Zeros are not required elsewhere.