Perimeter Calculator
Find the distance around a rectangle, triangle, circle, semicircle, sector (pie slice), polygon or any four-sided shape, in the unit you measured in.
Perimeter is the total length of a shape's outer edge, so for anything with straight sides you add the sides together. A rectangle 12 ft long and 10 ft wide has a perimeter of 2 x (12 + 10), which is 44 ft. For a circle the perimeter is the circumference, 2 x pi x the radius.
This calculator is for general education and planning. It assumes exact, flat shapes with straight sides or true circular arcs. Real fences, rooms and frames have corners, gaps and waste, so measure on site and add an allowance before you buy materials.
Perimeter
44 ft
- Inches
- 528
- Feet
- 44
- Yards
- 14.6667
- Centimeters
- 1,341.12
- Meters
- 13.4112
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About the Perimeter Calculator
Perimeter answers how much edge a shape has: the length of fence around a yard, trim around a window or ribbon around a frame. For straight-sided shapes it is plain addition. A rectangle has two lengths and two widths, so 12 ft by 10 ft gives 44 ft, which is 528 inches or 13.4112 meters. A triangle with sides 3, 4 and 5 has a perimeter of 12. A regular hexagon with 4 cm sides has 6 x 4, or 24 cm. Curves need pi. A circle of radius 5 has a circumference of 31.42. Cut it in half and the boundary is the curved half plus the straight diameter, 25.71. A quarter-circle slice of radius 10 has two straight radii plus a quarter of the circle, 35.71. Measure every side in the same unit before you enter it; the calculator then shows the total in inches, feet, yards, centimeters and meters using the exact definition, 1 inch = 2.54 cm.
Frequently asked questions
How do I find the perimeter of a rectangle?+
Add the length and the width, then double the total, because the shape has two of each. A 12 by 10 rectangle has a perimeter of 44 in the same unit you measured, so 12 ft by 10 ft gives 44 ft, or 528 inches.
Is perimeter the same as area?+
No. Perimeter is a length, the distance around the outside, so it is in feet or meters. Area is the space inside, in square feet or square meters. Use the area calculator on this site when you need flooring, paint or sod, and this page when you need fencing, edging or trim.
How do I find the perimeter of a semicircle?+
Take half of the circumference, which is pi times the radius, and add the diameter, which is twice the radius, because the flat edge is part of the boundary too. A semicircle of radius 5 comes to about 25.71.
Why does the calculator reject some triangles and four-sided shapes?+
Three sides make a triangle only when any two of them add up to more than the third. Four sides make a shape only when the longest side is shorter than the other three added together. If the lengths fail that test, no such shape exists, so there is no perimeter to report.
Formulas: based on OpenStax, Prealgebra 2e (2020): section 9.4 defines perimeter as the distance around a figure and gives P = 2L + 2W and P = a + b + c; section 9.5 gives C = 2 pi r. The semicircle, sector and polygon forms and the rules for which sides can close are worked out from that definition, not taken from the book.
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