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Area Calculator

By Lucas Meyer · Last updated 15 October 2026

You are standing in a room, wondering how much flooring it needs. The room is 12 metres long and 8 wide. Multiply them: 96 square metres. That is area, how much flat surface a shape covers, measured in square units. Pick your shape below and the calculator does the rest, formula included. Measure in one unit only. If your tape gives feet on one side and inches on the other, convert first so everything matches.

Enter your numbers

Result

Start With the Room You’re Standing In

Choose the shape: rectangle, square, circle, or triangle. Type the measurements in. The area comes out in square units: square metres if you entered metres, square feet if you entered feet.

The room example again, with the part people forget. Area = 12 × 8 = 96 m². This is the flooring example: a room this size needs 96 square metres of flooring before wastage. Most people add about 10% extra for cuts. That is 105.6 m² to order. Two more everyday sizes: a bedroom 4 m × 3.5 m → 14 m², and painting a wall 12 m × 8 m with two coats → 96 × 2 = 192 m² of coverage needed.

Every Shape, Its Formula

  • Rectangle: Area = Length × Width. A 12 m by 8 m room is 96 m².
  • Square: Area = Side × Side. A 5 ft square patio is 25 ft².
  • Circle: Area = π × Radius², with π ≈ 3.14159. Measure from the centre to the edge, which is the radius. Do not use the full width across (the diameter) by mistake.
  • Triangle: Area = ½ × Base × Height. The height must be measured straight up from the base, at a right angle, not along a slanted side.

Two More Shapes, Worked Through

A circle: radius 5 m. Area = π × 5² = 3.14159 × 25 = 78.5398… = 78.54 m². A round lawn or pond this size covers about 78 and a half square metres. A smaller one: a round rug with radius 1.2 m → 3.14159 × 1.44 = 4.52 m².

A triangle: base 10 m, height 6 m. Area = ½ × 10 × 6 = ½ × 60 = 30 m². A triangle is exactly half the rectangle it fits inside, which is where the ½ comes from. A smaller one: a triangular garden bed, base 6 m, height 4 m → 12 m².

The Three Mistakes

Three things trip people up. Mixing units: 12 feet by 8 inches is not 96 of anything until both sides share a unit. Using the diameter instead of the radius for a circle, which quadruples the answer. Measuring a triangle’s slanted side instead of its vertical height. Check those three and the maths takes care of itself.

One more: area and perimeter are different jobs. Area tells you how much surface there is: paint, flooring, turf. Perimeter tells you how long the edge is: fencing, skirting boards, edging. A 12 m × 8 m room has 96 m² of floor but 40 m of wall edge. If you are buying fencing, you want the edge, not the surface.

Area Questions, Answered

How do I calculate the area of a rectangle?

Multiply length by width. A 12 m by 8 m rectangle is 12 × 8 = 96 m². Both measurements must be in the same unit.

How do I find the area of a circle?

Multiply π (about 3.14159) by the radius squared: Area = πr². A circle with radius 5 m has an area of 78.54 m². If you only know the diameter, halve it first to get the radius.

What units is area measured in?

Square units of whatever you measured with: square metres (m²), square feet (ft²), square centimetres (cm²). The unit gets squared because you multiplied two lengths together.

What is the difference between area and perimeter?

Area is the surface inside the shape; perimeter is the distance around the edge. A 12 m × 8 m room has 96 m² of floor and a 40 m perimeter. Flooring uses area, fencing uses perimeter.

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