Perimeter Calculator
The distance around a yard, lot or any shape — rectangle, triangle, circle, polygon or a list of sides.
Perimeter is the total length of a shape's outside edge — the line you would walk, edge or fence. Pick the shape, enter its sides in feet, yards, meters or inches, and the calculator adds them up, converts the total to feet, yards and meters, gives the area inside where the shape defines one, and counts the posts for a closed fence line.
Calculation Results
An L-shaped or stepped yard with square corners has the same perimeter as the rectangle drawn around it: 2 × (overall length + overall width).
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🛠️ How This Calculator Works
Each shape uses its plane-geometry formula: a rectangle 2 × (L + W), a square 4 × side, any triangle a + b + c (area by Heron's formula), a right triangle a + b + √(a² + b²), a circle π × diameter, a regular polygon n × side, and any other shape the sum of its sides. Yards, meters and inches are converted to feet first (1 yd = 3 ft, 1 ft = 0.3048 m, NIST Handbook 44).
📐 Formula
Rectangle P = 2(L + W) · Square P = 4s · Triangle P = a + b + c · Right triangle P = a + b + √(a² + b²) · Circle C = πd · Regular polygon P = n × s · Posts (closed loop) = ⌈P ÷ spacing⌉📝 Example Calculation
A 100 × 60 ft back yard: P = 2 × (100 + 60) = 320 ft (106.7 yd, 97.5 m) Area = 100 × 60 = 6,000 sq ft Posts at 8 ft = 320 ÷ 8 = 40 A round garden 30 ft across: C = π × 30 = 94.2 ft
💡 Pro Tips from Fence Builders
- Measure each side along the ground where the fence or edging will run, not across the corners.
- For an L-shaped yard with square corners, the perimeter equals 2 × (overall length + overall width) — the notch adds nothing.
- An odd-shaped lot? Pick 'List of sides' and type every side in order, separated by commas.
- Fencing against the house or a neighbour's fence? Leave that side out — the linear footage calculator handles open sides and gates.
- A circle encloses the most area for its perimeter; a long thin rectangle the least.
Perimeter formulas
| Shape | Perimeter | Example | Result |
|---|---|---|---|
| Rectangle | 2 × (L + W) | 100 × 60 ft | 320 ft |
| Square | 4 × side | 50 ft side | 200 ft |
| Triangle | a + b + c | 30, 40, 50 ft | 120 ft |
| Right triangle | a + b + √(a² + b²) | legs 30 and 40 ft | 120 ft |
| Circle | π × diameter | 30 ft across | 94.2 ft |
| Regular hexagon | 6 × side | 10 ft sides | 60 ft |
Same area, different perimeter
Shape changes how much edge an area needs. Every row below encloses about 10,000 sq ft, but the fence line grows as the shape gets longer and thinner:
| Shape (≈10,000 sq ft) | Perimeter | Posts at 8 ft |
|---|---|---|
| Circle, 112.8 ft across | 354.5 ft | 45 |
| Square, 100 × 100 ft | 400 ft | 50 |
| Rectangle, 200 × 50 ft | 500 ft | 63 |
| Rectangle, 400 × 25 ft | 850 ft | 107 |
From perimeter to a fence
The perimeter is the starting point, not the order. Leave out any side that the house or an existing fence already covers and take off the gate openings with the fence linear feet calculator, then count posts with the fence post calculator and set their spacing with the post spacing calculator. For a large lot measured in acres, the acreage calculator gives the area from the same dimensions and the acreage to linear feet calculator goes the other way.
❓ Frequently Asked Questions
How do you calculate perimeter?
Add up the lengths of all the outside sides. For a rectangle that is 2 × (length + width): a 100 × 60 ft yard has a 320 ft perimeter. For a circle it is π × the diameter: 30 ft across is 94.2 ft around.
What is the perimeter of a triangle?
The sum of its three sides. Sides of 30, 40 and 50 ft give 120 ft. For a right triangle you only need the two legs: 30 and 40 ft make a 50 ft hypotenuse (√(30² + 40²)), so the perimeter is 120 ft.
What's the difference between perimeter and area?
Perimeter is a length — the distance around — measured in feet or meters. Area is the surface inside, in square feet or square meters. A 100 × 60 ft yard has a 320 ft perimeter but a 6,000 sq ft area.
How do I find the perimeter of an L-shaped yard?
If all the corners are square, it equals the perimeter of the rectangle that just encloses it: 2 × (overall length + overall width). An L that is 80 ft by 50 ft overall has a 260 ft perimeter however deep the notch. Otherwise, list every side and add them.
How many fence posts do I need around a perimeter?
On a closed loop, one per section: perimeter ÷ post spacing, rounded up. 320 ft at 8 ft spacing is 40 posts. Add a post on each side of every gate; the linear footage and post calculators handle gates and open runs.
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