Perimeter Calculator

Perimeter is the total distance around the boundary of a two-dimensional shape. Imagine tracing every outside edge once and adding the distances you travel. That sum is the perimeter. For a curved boundary such as a circle, the corresponding term is circumference, but it represents the same basic measurement: the length of the complete boundary. A rectangle has two pairs of equal opposite sides, so its perimeter is twice the sum of its length and width. A rectangle that is 8 units long and 5 units wide has perimeter 2 × (8 + 5), or 26 units. A square is a special rectangle whose four sides are equal. Its formula simplifies to four times the side length, so a square with side 7.5 units has a perimeter of 30 units. For a circle, the circumference depends on pi. You can multiply the radius by 2π, or multiply the diameter by π. The calculator uses the browser's full stored precision for pi and rounds only the displayed result. A radius of 3 gives a circumference of approximately 18.849556 units. Because pi is irrational, most circular results are decimal approximations rather than terminating values. Perimeter always uses linear units. If dimensions are entered in centimeters, the result is centimeters, not square centimeters. Square units belong to area, which measures the surface enclosed by the boundary. Keeping this distinction clear is important in construction, landscaping, sewing, manufacturing, and geometry homework. Fence length is a perimeter problem; the amount of turf inside the fence is an area problem. All inputs must use the same unit before calculation. If a rectangle's length is given in meters and its width in centimeters, convert one measurement so both match. The calculator labels the answer generically as units because it cannot know which unit you selected. Decimal dimensions are supported, making the tool useful for practical measurements as well as textbook integers. Use this perimeter calculator for quick planning and verification. Select the matching shape, supply its required dimensions, and compare the result with the formula shown beneath it. For irregular polygons, measure and add every side individually; for composite boundaries, split the outline into known straight and curved pieces, calculate each exposed piece, and add them without counting internal shared edges.