The perimeter of a shape is the total length of its outer boundary — the distance you would walk if you traced every edge and came back to where you started. It sounds abstract, but in practice it is the number that drives fencing quotes, trim and molding budgets, baseboards, garden edging, and the border around a rug or a pool. This calculator handles the four shapes people actually measure in real life — the rectangle, the square, the triangle, and the circle — and converts the result into feet, yards, and meters so you can order materials without a second spreadsheet.
Pick a shape, type your numbers in feet, and the outer boundary length updates instantly. Switch the shape and the same form adapts: a rectangle needs a length and a width, a square needs a single side, a triangle needs all three sides, and a circle needs only its radius.
How to Use
- Choose your Shape from the dropdown — rectangle, square, triangle, or circle.
- Enter the Length / Side / Radius in feet. For a rectangle this is the long side; for a square it is the only side; for a triangle it is side A; for a circle it is the radius.
- Enter the Width / Side B in feet. For a rectangle this is the short side; for a triangle it is side B. Leave it alone for a square or a circle — it is ignored.
- For a triangle only, enter Side C. If you only know the circle's diameter, divide it by two and type the radius into the first field.
- Read the result card: the main Perimeter is shown in feet, with the enclosed Area, plus Yards and Meters conversions below it.
- Multiply the boundary length by your material price per foot — for example vinyl fencing at $8 per linear foot, or baseboard molding at $1.50 per foot — to estimate the total cost of edging the space.
If you measured in meters instead of feet, convert first: one meter is about 3.281 feet, and one yard is three feet. The formulas themselves do not change — only the unit your answer arrives in.
The Perimeter Formulas
Each shape uses a standard geometry formula taught in middle school and still used by builders, landscapers, and architects:
- Rectangle: Perimeter = 2 × (length + width). A yard that is 12 feet long and 8 feet wide has an outer boundary of 2 × (12 + 8) = 40 feet.
- Square: Perimeter = 4 × side. A square room with a 12-foot side is surrounded by 4 × 12 = 48 feet of edge.
- Triangle: Perimeter = side A + side B + side C. A triangular garden bed with sides of 3, 4, and 5 feet is edged by 3 + 4 + 5 = 12 feet.
- Circle (circumference): Perimeter = 2 × π × radius. With π ≈ 3.14159, a circular patio of radius 5 feet has a boundary of 2 × 3.14159 × 5 ≈ 31.42 feet.
Once you have the feet figure, conversions are fixed: divide by three to get yards, and multiply by 0.3048 to get meters. A 40-foot boundary is therefore 13.33 yards, which is why fencing sold by the yard costs roughly three times the per-foot price tag on the label.
Perimeter vs. Area: Know the Difference
Perimeter and area are easy to confuse, but they answer opposite questions. Perimeter measures the distance around the outside — one-dimensional, measured in feet. Area measures the space inside the boundary — two-dimensional, measured in square feet.
The same 12-by-8-foot room has a perimeter of 40 feet (the baseboard you would install) but an area of 96 square feet (the carpet you would lay). Fencing and trim depend on the perimeter; flooring and paint depend on the area. Mixing them up is one of the most common quoting mistakes, which is why this page deliberately shows the boundary length rather than the enclosed space.
When to Use Which Shape
Real spaces are rarely a single perfect shape. A fenced backyard is a rectangle; a square deck needs four equal sides; a gable end or a triangular planting bed is a triangle; a circular patio or a pool surround is a circle. The practical trick is to split a complex yard into rectangles, triangles, and circles, measure each boundary separately, then add the perimeters together — but remember to subtract any shared internal edge that is not actually fenced.
Land in the US is usually described by its total area in acres, but fencing contractors price their work by the linear foot of outer boundary. That is exactly why this calculator shows the boundary length alongside its yard and meter conversions: a lot of 2,000,000 by 800 feet has a perimeter of 4,001,600 feet — roughly 1,333,867 yards or about 1,219,688 meters — which is the number a fencing quote is built on. (For a typical 200-by-80-foot residential lot, by contrast, the perimeter is just 2 × (200 + 80) = 560 feet.)
Examples
Example 1 — Fencing a backyard. A rectangular yard measures 120 feet by 80 feet. Select rectangle, enter side1 120 and side2 80. The perimeter is 2 × (120 + 80) = 400 feet, which equals 133.33 yards. At $8 per linear foot for vinyl fencing, the outer edge costs about 400 × $8 = $3,200 — plus gate hardware and corner posts on top.
Example 2 — Edging a square deck. A square deck has a side of 12 feet. Select square, enter side1 12. The perimeter is 48 feet, or 16 yards. If you want composite trim around the rim at $1.50 per foot, the edging runs about 48 × $1.50 = $72.
Example 3 — Borders around a triangular flower bed. A triangular bed has sides of 3, 4, and 5 feet. Select triangle, enter side1 3, side2 4, side3 5. The perimeter is 12 feet, which is the length of steel garden edging you would need to order.
Example 4 — A circular patio. A circular patio has a radius of 5 feet. Select circle (round), enter the radius 5 into the first (Length / Side / Radius) field. The circumference is 31.42 feet, the enclosed area is 78.54 sq ft, and it converts to about 10.47 yards. A curbing contractor charging $10 per linear foot would quote roughly 31.42 × $10 = $314 to edge the curve.
Example 5 — Measuring a very large parcel. A rectangular lot measures 2,000,000 feet by 800 feet. Select rectangle, enter side1 2000000 and side2 800. The perimeter is 4,001,600 feet, which converts to about 1,333,867 yards or 1,219,688 meters — the scale used for large land and boundary surveys.
FAQ
What is the difference between perimeter and area?
Perimeter is the total distance around the outside of a shape, measured in linear units like feet. Area is the amount of space inside that boundary, measured in square units like square feet. Fencing, trim, and edging depend on the perimeter; flooring, paint, and sod depend on the area.
How do I calculate the perimeter of a rectangle?
Add the length and the width, then double the sum: Perimeter = 2 × (length + width). For a rectangle that is 12 feet by 8 feet, the perimeter is 2 × (12 + 8) = 40 feet.
What is the perimeter of a circle called?
It is called the circumference, and it is calculated as 2 × π × radius, or π × diameter. For a circle with a radius of 5 feet, the circumference is about 31.42 feet. If you know the diameter instead, just multiply the diameter by π.
How do I find the perimeter of a triangle?
Add all three side lengths together: Perimeter = side A + side B + side C. A triangle with sides of 3, 4, and 5 feet has a perimeter of 12 feet. If you only know two sides and the included angle, use the law of cosines to find the third side first.
How do I convert perimeter in feet to yards or meters?
There are three feet in a yard, so divide the foot figure by three. One foot equals 0.3048 meters, so multiply by 0.3048. A 40-foot perimeter is 13.33 yards and about 12.19 meters. This calculator shows all three units automatically.
Why is perimeter used for fencing quotes?
Fencing and edging materials are sold and installed by the linear foot or linear yard, not by the acre. A contractor prices each post and each panel along the outer boundary, so the total cost depends on the perimeter, not the area inside it. Always measure the boundary length before you request a fence quote.
Disclaimer
This perimeter calculator is provided for informational purposes only and does not constitute architectural, engineering, surveying, or construction advice. Results are rounded to two decimal places. Results assume accurate linear measurements in feet and the standard planar geometry formulas; complex, curved, sloped, or irregular boundaries may require a professional survey. Always double-check your measurements and confirm material quantities and quotes with your contractor before ordering. For our editorial standards see the About page, and for data handling see the Privacy Policy; we do not store the dimensions you enter on this page.