Perimeter of a Rectangle Calculator
Calculate the perimeter of a rectangular area from its length and width — for fencing, edging, trim, or baseboard runs.
How this calculator works
Perimeter is the total distance around the outside edge of a rectangular space. For any material that runs along that edge — fencing, edging, baseboard, or trim — perimeter is the number you need, not the square footage of the space itself.
Formula: Perimeter = 2 × (length + width).
Worked example
A 20 ft × 12 ft rectangle:
- Perimeter: 2 × (20 + 12) = 64 ft
Notes
Perimeter is the number to use for anything that runs around the edge of a space — fencing, edging, baseboard, or trim. Area, which is length × width, is for anything that covers the whole surface, like flooring or sod. These two numbers measure different things and aren’t interchangeable, so it’s worth double-checking which one a given material is priced by before ordering.
A rectangle only needs two measurements to find its perimeter — the length and the width — because the two long sides match each other and the two short sides match each other. That’s why the formula doubles the sum of just one length and one width instead of adding up four separate side measurements.
For spaces that aren’t simple rectangles, this formula doesn’t apply directly. An L-shaped yard or a room with a jog in the wall still has a perimeter, but it’s found by measuring the full outer boundary, straight run by straight run, and adding those runs together rather than treating it as a single rectangle.
How to use
Enter the length and width of the rectangular space in feet. The calculator doubles their sum to return the total perimeter, which you can then use to order fencing, edging, baseboard, or trim for the full run around the space.
A pure geometry calculation. Always double-check real-world measurements before ordering material.
Frequently asked questions
What's the formula for the perimeter of a rectangle?
Perimeter equals 2 times the sum of the length and the width: 2 × (length + width). This works because a rectangle has two long sides and two short sides, so adding one of each and doubling the total accounts for all four sides.
What's the difference between perimeter and area?
Perimeter is the distance around the outside edge of a space, measured in a single unit like feet. Area is the amount of surface the space covers, measured in square units like square feet. Fencing and edging need perimeter; flooring and sod need area — they aren't interchangeable.
Do I need to measure all four sides of a rectangle?
No. Since a rectangle has two pairs of equal sides, you only need to measure one length and one width. The formula 2 × (length + width) accounts for both matching sides automatically, so there's no need to walk and measure all four edges separately.
Does this work for a space that isn't a perfect rectangle?
Not directly. For an L-shaped or irregular space, break it into rectangular sections, find the perimeter of the full outer boundary by measuring each straight run of the outline, and add those runs together rather than applying this formula to each sub-rectangle separately.
Estimates only. Verify quantities with your supplier before purchasing.