How to Measure a Room and Work Out Flooring or Paint

Measure area the right way, convert between square metres and square feet, add a waste allowance, and turn area into a materials cost.

Last updated: September 2026

Whether you are laying flooring, tiling or buying paint, the job starts with area. For a rectangular room that is just length × width — but the details (odd shapes, waste, unit conversions) are where budgets go wrong.

The basic area

Area = length × width. A room 4 m by 3 m is 12 m². In feet, a 13 ft by 10 ft room is 130 ft². Keep both sides in the same unit before multiplying.

Square metres and square feet

Because 1 foot = 0.3048 m exactly, one square foot is 0.3048² = 0.092903 m², and one square metre is 10.7639 ft². So multiply ft² by 0.092903 to get m², or m² by 10.7639 to go the other way. A 12 m² room is 12 × 10.7639 = 129.2 ft².

Odd shapes

Split an L-shaped room into two rectangles, work out each area, and add them. For a bay or alcove, do the same. For anything triangular, area is ½ × base × height.

Always add a waste allowance

Never buy exactly the area you measured. Cuts, breakages and pattern matching mean you need extra — commonly around 5–10% for flooring and tiles, more for diagonal layouts or busy patterns. On 20 m² of flooring, a 10% allowance means buying 22 m².

From area to cost

Once you have the area (plus waste), the cost is area × price per unit. 22 m² of flooring at 25 per m² is 22 × 25 = 550. Paint is sold by coverage per litre, so divide the wall area by the litres-per-can coverage to see how many cans you need, and remember two coats.

Measure and cost in one step

The area calculator gives the room area in both m² and ft² and turns it into a flooring, tile or paint cost from a price per unit — add your own waste percentage on top.