Calculate construction area

This construction area calculator works out the area of any rectangular space from its length and width. Enter the dimensions in metres, feet, or yards and it returns the area in square metres, square feet, and square yards, plus the perimeter. It is ideal for estimating flooring, tiling, paint, decking, turf, slabs, and other materials sold by area.

How to measure area

For a rectangle, area = length × width. For an L-shaped or irregular space, split it into rectangles, calculate each part, and add them together. Always measure at the widest points and add about 10% extra when ordering materials to allow for cuts, waste, and breakages.

Estimating materials by area

Once you know the area, you can estimate quantities: paint coverage is usually given in m² per litre, tiles and turf are sold per m², and decking per linear or square metre. For depth-based materials like concrete and gravel, use our concrete calculator and gravel calculator, which factor in thickness.

How to work out the area of construction

The area of construction (sometimes called the built-up or covered area) is the total floor area a structure occupies, measured to the outside face of the external walls. For a simple rectangular building it is just length × width. For an L-shaped or irregular plan, split the outline into rectangles, work out each area, then add them together — subtracting any courtyards, lift shafts or open voids that are not built over. Multi-storey buildings multiply the footprint by the number of floors.

Worked example: a house measuring 12 m × 8 m with a 4 m × 3 m rear extension has a footprint of (12 × 8) + (4 × 3) = 96 + 12 = 108 m², which is about 1,163 ft². Over two storeys the total construction area is 216 m². Quantities for materials follow from this figure, so it is worth measuring twice — use the calculator above to convert between square metres and square feet as you go.

Frequently asked questions

How do I calculate square metres?

Multiply the length by the width, both measured in metres. A room 5 m long and 4 m wide is 20 m².