Perimeter Calculator
Find the perimeter of squares, rectangles, triangles, circles and parallelograms in seconds, with the semi-perimeter included.
Perimeter
20
Semi-perimeter
10
Half the perimeter, used in Heron's formula
The perimeter is the total distance around the shape. For a circle it is called the circumference, found as 2πr.
Perimeter Calculator on True Calculator gives you an instant, accurate answer with no sign-up and no app install. Find the perimeter of squares, rectangles, triangles, circles and parallelograms in seconds, with the semi-perimeter included. Every result shows the formula and a worked example so you can verify the calculation yourself, and all values are computed in your own browser — your numbers never leave your device.
Popular uses: perimeter calculator · perimeter of a rectangle · perimeter of a triangle
How We Calculate
This calculator uses standard mathematical formulas — the same ones taught in school and used in exams — verified by our team. All calculations are performed instantly in your browser using JavaScript, so no data is sent to any server.
The formulas follow standard mathematical definitions and conventions used in textbooks and by educational boards. Results are rounded transparently and shown with the exact formula on this page.
When to Use This Calculator
Perimeter is the measurement you reach for whenever something must go around the outside of a shape. In India, that means fencing a plot or balcony railing, quoting for compound-wall boundary work, estimating pipe or cable length for a layout, or buying paper edging for school projects. Municipal approvals and property documents often list plot dimensions, and this calculator converts those dimensions into the running-metre quantity contractors price per metre. It is equally useful for tailoring — a saree border or dupatta edging needs the perimeter of the garment piece — and for framing: the frame length around a photo or mirror equals its perimeter. Students use it constantly while solving mensuration problems, where checking the perimeter of a rectangle or triangle against a hand calculation takes seconds.
How to Use This Calculator
- Step 1: Pick the shape — square, rectangle, triangle, circle or parallelogram.
- Step 2: Enter the side lengths, or the radius for a circle, in any unit such as metres, feet or inches.
- Step 3: Read the perimeter (the circumference for a circle) in the same unit you entered.
- Step 4: Use the semi-perimeter shown below it when working with Heron's formula or inscribed-circle problems.
Worked Example
A homeowner in Bengaluru wants to fence a rectangular plot that is 12 m long and 8 m wide. Selecting the rectangle shape and entering 12 and 8 gives a perimeter of 2 × (12 + 8) = 40 m, which is the exact fencing length to buy. The same plot's semi-perimeter is 20 m. For a circular garden bed with radius 35 cm, the tool reports a circumference of about 219.91 cm — enough rope to edge it completely. Triangle plots, common in corner layouts, simply need all three side lengths added.
Tips and Common Mistakes
- •Tip 1: Keep all inputs in one unit — mixing metres and centimetres will make the result wrong by a factor of 100.
- •Tip 2: For a rectangle you only need length and width; the tool multiplies the sum by 2 for you.
- •Tip 3: When buying fencing or edging, add 5–10% extra for overlaps, corners and cutting waste.
- ✗Mistake 1: Entering the diameter where the radius is expected for a circle, which halves the circumference.
- ✗Mistake 2: Confusing perimeter with area — 40 m of fencing is a length, not the 96 m² the plot covers.
Frequently Asked Questions
What is the perimeter of a shape?
The perimeter is the total distance around the outside of a shape, found by adding up all its sides. For a rectangle with length 4 and width 7, the perimeter is 2 × (4 + 7) = 22 units.
How do I find the perimeter of a rectangle?
Add the length and width, then multiply by 2: perimeter = 2 × (length + width). A plot that is 12 ft by 8 ft has a perimeter of 2 × (12 + 8) = 40 ft, which is the fencing length you would need.
What is the difference between perimeter and circumference?
Both measure the distance around a shape. Circumference is the specific name used for a circle, calculated as 2πr, while perimeter is used for polygons. A circle with radius 7 has a circumference of about 43.98 units.
What is the semi-perimeter used for?
The semi-perimeter is exactly half the perimeter. It appears in Heron's formula for the area of a triangle and in formulas for inscribed circles, so many students and builders use it alongside the perimeter.
Can the perimeter be smaller than the area?
Yes — perimeter and area are different units (length versus squared length), so the numbers cannot be compared directly. A small square of side 0.5 has perimeter 2 but area only 0.25, while a large square behaves the opposite way.
You might also need
Related calculators from other categories
Construction
BTU Calculator
Calculate the BTU and AC tonnage required for a room based on size, sun exposure and insulation.
Construction
Concrete Calculator
Calculate concrete volume, weight and number of cement bags for a slab. Get exact quantities for your construction project.
Construction
Gravel Calculator
Estimate gravel volume, weight in tonnes and 50 kg bags for driveways and paths by material density.
Construction
Mulch Calculator
Work out mulch volume in m³ and litres, plus bags needed and cost for your garden beds.