Area Calculator
Find the area and perimeter of rectangles, circles and triangles.
Area
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Perimeter
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Diagonal / extra
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Area and perimeter formulas
| Rectangle | Area = length × width · Perimeter = 2 × (length + width) |
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| Circle | Area = π × radius² · Circumference = 2 × π × radius |
| Triangle | Area = √(s(s−a)(s−b)(s−c)) where s = (a+b+c) ÷ 2 |
Area is always in square units (m², ft²) and perimeter in the linear unit. To find square footage for flooring or paint, use the rectangle option and read the area.
Worked example
A room 10 ft by 5 ft has an area of 50 square feet and a perimeter of 30 feet. A circle with a 5 m radius has an area of pi times 5 squared, which is about 78.54 square metres.
From area to materials
Area is the bridge between a measurement and a shopping list. Flooring, tiles, turf and paint are all sold by coverage, so once you know the area you can work out how much to buy — then add a margin for cuts, breakages and the occasional mistake.
Tips for real rooms
- Add about 10% for waste on flooring and tiling; more for diagonal or patterned layouts.
- Break odd shapes up. Split an L-shaped room into rectangles, work out each, and add them together.
- Paint lists a coverage per litre or gallon — divide your wall area by that figure, and don't forget a second coat.
Frequently asked questions
How do I find square footage for flooring?
Use the rectangle option with the room's length and width; the area is your square footage. Add about 10% for cuts and waste when ordering.
Why does the triangle option use three sides?
With all three sides, Heron's formula gives the area directly and the perimeter is simply their sum, so you do not need to measure the height.
What if my room is not a simple shape?
Split it into rectangles and triangles, calculate each piece, and add the areas together for the total.
What is the difference between area and perimeter?
Area is the surface inside the shape, measured in square units, while perimeter is the distance around its edge, measured in linear units.