Area and Perimeter Calculator
Pick a shape, enter its measurements and instantly get the area and perimeter, along with the formulas used for the calculation.
Formulas:
The area is in square units of whatever you entered (e.g. in → sq in, ft → sq ft), the perimeter in the same unit as the sides.
When you need area and when you need perimeter
The perimeter is the length of the outline: that's what you need for fencing, baseboards, picture frames, garden edging or an LED strip along a wall. The area measures the surface inside: that's what you need for flooring and tile, paint for a wall, sod for a lawn, fabric and tablecloths. For a circle the "perimeter" is called the circumference (2·π·r), and for a rhombus this tool derives the side from the two diagonals using the Pythagorean theorem: side = √((D/2)² + (d/2)²).
Watch your units
Before you calculate, convert every measurement to the same unit: if the base is in feet and the height in inches, the result will be off by a factor of 12. Also remember that area comes in square units: a room 12 ft by 10 ft has an area of 120 sq ft, which is 17,280 sq in — not 1,440. The tool works just as well with metric units (m → m², cm → cm²). For a triangle, the height is the perpendicular distance from the base to the opposite vertex, not one of the slanted sides.