BuildCalcs Square Metre Calculator
Calculate m² and ft² for one room, several rooms or an L-shaped space. Enter each section in metres, centimetres or feet, then add an optional material allowance.
Measure your rooms
Add a rectangle for each room or section. For an L-shaped room, use two rectangles that do not overlap.
How to calculate square metres (m²)
For a rectangle, multiply its length by its width. When both measurements are in metres, the answer is in square metres:
Area in m² = length in metres × width in metres
A room measuring 4m × 3m has an area of 12m². Square metres measure surface area, while metres measure length: a single measurement of 4m is not enough to calculate an area.
Use metres, centimetres or feet
Choose the unit beside each room before entering your measurements. You can mix units between rooms: for example, enter one room in metres and a hallway in centimetres. If you change a room's unit later, the entered length and width are converted for you.
| Measurements | Calculation | Area |
|---|---|---|
| 4m × 3m | 4 × 3 | 12m² |
| 450cm × 320cm | 4.5 × 3.2 | 14.4m² |
| 10ft × 12ft | 120ft² × 0.09290304 | 11.15m², rounded |
For centimetres, divide each length by 100 before multiplying, or divide the resulting cm² by 10,000. One foot is 0.3048m, so one square foot is 0.09290304m². Enter feet as decimals: 10ft 6in is 10.5ft.
Add several rooms or an L-shaped room
Use Add another room / section for each rectangle and give it a name if helpful. Press Calculate total area to see each section and the combined area. You can edit or remove sections before recalculating.
For an L-shaped room, draw a line across the shape to divide it into two non-overlapping rectangles. If section A is 4m × 3m and section B is 2m × 1.5m, the total is 12 + 3 = 15m². Keep a sketch so a corner or connecting section is counted only once.
Measured area and material allowance
The measured area is the space you have entered. Material allowance adds extra coverage for cutting and layout; it does not increase the size of the room. The calculator applies one percentage to the combined measured area and shows both totals separately.
For the 15m² L-shaped example, a 10% allowance adds 1.5m², giving 16.5m² including allowance. The 10% starting value is editable, not a recommendation for every material. Set it to 0 when you only need the measured area.
For flooring and tiles, pack coverage and layout affect the amount to buy. Use the flooring calculator or tile calculator for product quantities. For wall paint, use the paint calculator to account for room height, openings, coats and coverage.
Frequently asked questions
Can I use a different unit for each room?
Yes. Choose metres, centimetres or feet for each room. The calculator converts the areas and provides a combined total in both m² and ft².
How do I calculate an L-shaped room?
Split the floor plan into two rectangles that do not overlap, add one section for each rectangle and calculate the combined area. Do not use the full outer length multiplied by the full outer width, because that would include the missing corner.
How many square feet are in one square metre?
One square metre is approximately 10.764 square feet. Multiply m² by 10.764 to estimate ft², or multiply ft² by 0.09290304 to obtain m².
Does the calculator include material waste?
It shows measured area and area including your chosen allowance separately. The allowance is applied once to the total of all sections. Use 0% to keep both totals equal.
Is square meter the same as square metre?
Yes. Square metre is the UK spelling and square meter is the US spelling. Both use m² and describe the same unit of area.