The method

How this calculator works

Multiply the two sides

The area of a rectangle is its length times its width. Multiply them in metres to get square metres, so a 4 m by 3 m room is 12 m². If you measured in centimetres, divide each side by 100 first, or switch the unit selector to centimetres and let the calculator convert for you.

For a triangle, multiply the base by the straight-line height and halve it. For a circle, the area is about 3.14 times the radius times the radius, and the radius is half the diameter.

Split awkward shapes into simple ones

Few rooms are perfect rectangles. For an L-shaped room, measure the whole outline as if it were a rectangle, then subtract the missing corner. This calculator does that for you. Alternatively, split the room into two rectangles and add their areas.

For a room with several alcoves or a bay, work out each rectangle separately and add them up. Sketch the shape on paper and write each measurement on the sketch so nothing is missed.

Square units do not convert like lengths

One metre is about 3.28 feet, but one square metre is about 10.76 square feet, because the conversion applies to both sides. Multiplying an area in square metres by 3.28 gives the wrong answer; multiply by 10.764 instead. In the other direction, divide square feet by 10.764 to get square metres.

UK carpet is sometimes priced per square yard, and 1 m² is about 1.196 square yards. The calculator shows square metres, square feet and square yards together so you can compare prices quoted in any of them.

Worked example

Example: a 4 m × 3 m room

  1. Multiply the length by the width: 4 × 3 = 12 m².
  2. Convert to square feet: 12 × 10.764 = 129.2 sq ft.
  3. Convert to square yards: 12 × 1.196 = 14.35 sq yd.
  4. The perimeter is 2 × (4 + 3) = 14 m, which is also the length of wall you would measure for skirting boards before taking off doorways.

Practical answer: The room is 12 m², which is about 129 sq ft or 14.4 sq yd. Add a waste allowance when you buy materials, for example 10% for flooring would take 12 m² to 13.2 m².

Before you buy

Common measuring mistakes

  • Mixing units, such as entering the length in metres and the width in centimetres.
  • Converting square metres to square feet by multiplying by 3.28 instead of 10.764.
  • Entering the radius of a circle in the diameter box, which makes the area four times too small.
  • Using the length of a sloping side instead of the straight-line height for a triangle.
  • Forgetting alcoves, bays or a hallway that will be covered as well as the main room.
  • Ordering exactly the area with no allowance for cuts and waste.