Rectangle Perimeter Calculator
Find the distance around a rectangle from its length and width. The perimeter adds all four sides and returns an ordinary length.
How to use Rectangle Perimeter Calculator
1. Choose Measurement Unit, then enter Length, Width without a unit suffix. 2. Use the selected ordinary, square or cubic unit for each measurement as explained below; changing the selector relabels inputs and does not convert them. 3. Select Calculate, or press Enter, and read rectangle perimeter. 4. Select Select Copy result to copy the answer, or Reset to clear the form.
Why use this tool?
Estimate edging, a frame or boundary material around a rectangular feature before adding joints or overlaps.
How the calculation works
Perimeter = 2 × (length + width), because the two opposite pairs of sides have equal lengths. Results use up to six decimal places. Tiny nonzero results below 0.000001 use scientific notation with six significant digits. Browser floating-point arithmetic can introduce small rounding differences. Inputs and calculated magnitudes must not exceed 9,007,199,254,740,991. Negative physical measurements and arithmetic underflow are rejected. Zero dimensions are treated as a degenerate limit where the formula allows them; divisors and sides of an actual triangle must be positive. Formula reference: https://openstax.org/books/prealgebra-2e/pages/c-geometric-formulas
Example
Length = 12 cm and Width = 8 cm give 2 × (12 + 8) = 40 cm.
Practical tip
Use the boundary dimensions where the material will sit. An inner and outer frame can have different perimeters.
Frequently asked questions
Is perimeter measured in square units?
No. Perimeter is a total length. A cm input gives cm, while rectangle area would be measured in cm².
Does this allow for corner joints?
It adds the geometric side lengths only. Joint, cut and overlap allowances depend on the material and construction method.
Does changing Measurement Unit convert my numbers?
No. The selector states the unit of the numbers you enter and labels the answer. Convert measurements first when changing units. Area inputs use square units and volume inputs use cubic units; result precision follows the rounding method above.