How to Work Out Area: Rooms, Walls and Gardens in Square Metres
Whether you are buying flooring, ordering paint, laying a patio or turfing a lawn, the first job is always the same: work out the area. Get it right and you buy just enough material; get it wrong and you are making extra trips to the shop or paying for waste. This practical guide shows how to work out area in square metres for everyday spaces such as rooms, walls, gardens and awkward L-shapes, including the allowances professionals add for cutting and waste.
The Quick Method for Working Out Area at Home
Almost every home project can be handled with one simple routine. If you are wondering how do I work out an area for the first time, follow these steps and write everything down as you go.
- Sketch the space. A rough drawing with the shape marked on it is enough.
- Measure each wall or edge in metres. Use two decimal places, for example 3.65 m.
- Split awkward shapes into rectangles. Label them A, B and C.
- Multiply length by width for each rectangle.
- Add the pieces (and subtract any holes, such as a chimney breast or a pond).
- Add an allowance for waste using the table later in this guide.
The underlying formulas are explained in How to Calculate Area, and How to Find Area covers methods for curved and irregular outlines. This page focuses on practical jobs around the home and garden.
What You Need to Measure an Area Accurately
You do not need specialist equipment, but the right tool saves time and reduces mistakes.
- Tape measure (5 m or longer): fine for single rooms. A rigid, wide blade is easier to use alone.
- Laser distance measurer: measures a wall length in one second, ideal for large rooms.
- Measuring wheel: best for long garden paths, driveways and boundaries.
- Notepad or phone: write down the measurement the moment you take it.
- Calculator or an online tool: our Area Calculator handles rectangles, triangles, circles and more, so you can double-check by hand.
How to Work Out the Area of a Room
A Simple Rectangular Room
Multiply the length by the width. A bedroom that is 4.2 m long and 3.6 m wide has an area of 4.2 × 3.6 = 15.12 m². In square feet that is 15.12 × 10.764 = about 162.8 ft².
An L-Shaped Room
Draw a line that divides the L into two rectangles. If the main part is 5 m × 4 m and the extension is 2.5 m × 3 m, then Area A = 20 m² and Area B = 7.5 m². The total is 27.5 m². You can divide the L in two different ways; both give the same answer, so use the second way as a check.
A Room with an Alcove or Bay
Treat the alcove as an extra small rectangle and add it. A 4 m × 3.5 m room has 14 m². A 1.2 m wide, 0.6 m deep alcove adds 0.72 m², giving 14.72 m². For a room with a chimney breast that sticks out, work out the full rectangle and subtract the area the breast occupies, unless you plan to cover that floor as well.
A Room with a Curved or Angled Wall
A curved bay is roughly a semicircle or a trapezoid, so use ½ × π × r² or ½ × (a + b) × h. Details for curved and unusual outlines are in Area of a Heart, Oval and Curved Shapes.
Lounge: 5.4 m × 3.9 m = 21.06 m². Bay window recess: 1.8 m × 0.5 m = 0.9 m². Total floor area = 21.96 m².
Add 10% for cutting waste: 21.96 × 1.10 = 24.16 m². If one pack covers 2.2 m², you need 24.16 ÷ 2.2 = 10.98, so buy 11 packs.
How to Work Out the Area of Walls for Painting or Wallpaper
Wall area is a little different from floor area because you must subtract the parts you will not paint, such as windows and doors. The easiest approach is to work out the whole perimeter of the room first, multiply by the wall height, then take away openings.
Perimeter = 2 × (4.2 + 3.6) = 15.6 m.
Gross wall area = 15.6 × 2.4 = 37.44 m².
Door = 0.8 × 2.0 = 1.6 m²; window = 1.2 × 1.0 = 1.2 m²; total openings = 2.8 m².
Paintable wall area = 37.44 − 2.8 = 34.64 m².
Two coats = 69.28 m². If the paint covers about 12 m² per litre (check the tin), you need 69.28 ÷ 12 = 5.8 litres, so buy 6 litres.
Ceiling (if painting): 4.2 × 3.6 = 15.12 m², or about 30.2 m² for two coats.
Skirting boards, picture rails and large pieces of fixed furniture can be ignored for rough estimates, but include them if you are buying expensive paint or wallpaper. Patterned wallpaper also needs extra for matching, usually around 10–15%.
How to Work Out Areas in the Garden: Lawns, Patios and Beds
Garden spaces are rarely a single rectangle. Beds curve, paths wiggle and trees stand in the way. The reliable approach is to divide the garden into regular shapes, as shown below.
Lawn and Turf
A rectangular lawn that is 12 m by 8 m has 96 m². If a 2 m × 3 m flower bed sits inside it, the grass area is 96 − 6 = 90 m². Turf is often sold in rolls of 1 m² (check your supplier), so you need about 90 rolls, plus 5% to allow for trimming and settling: 90 × 1.05 = 94.5, so order 95 rolls.
Patio and Paving
A 4 m × 3 m patio is 12 m². If you use 0.6 m × 0.6 m slabs, each covers 0.36 m², so you need 12 ÷ 0.36 = 33.3 slabs. Round up and add 10% for cuts and breakages: 33.3 × 1.10 = 36.7, so order 37 slabs. Also allow for mortar joints and the sub-base, which does not change the surface area but does change the volume of sand and stone you need.
Circular Features
A round pond with a diameter of 2.4 m has a radius of 1.2 m, so its area is 3.14159 × 1.2² = 4.52 m². A circular lawn of radius 4 m has an area of 50.27 m².
If you plan to pour concrete for a base or path, multiply your area by the thickness to get volume; our Concrete Calculator does that and converts to bags and cubic metres.
How to Work Out How Many Tiles, Planks or Rolls You Need
Once you know the area, converting it into product quantities is just division.
Floor: 3.2 m × 2.5 m = 8 m². One tile measures 30 cm × 30 cm = 0.09 m².
8 ÷ 0.09 = 88.9, so 89 tiles for the exact area. Adding 10% for cuts gives 89 × 1.10 = 97.9, so buy 98 tiles.
Do not forget to convert centimetres to metres before you divide. A 30 cm tile is 0.3 m, so its area is 0.3 × 0.3 = 0.09 m², not 900 cm² mixed with metres. For round and pattern-heavy jobs, ask your supplier for the recommended allowance.
How Much Extra Should You Add for Waste?
Real jobs always need slightly more material than the area on paper, because of off-cuts, breakages, pattern matching and mistakes. The chart shows typical allowances (the middle of the usual range). Always follow the manufacturer’s advice for your product.
| Job | Typical allowance | Why |
|---|---|---|
| Laminate, vinyl, engineered wood | 5–10% | Cut-offs at walls and awkward corners |
| Straight-laid ceramic tiles | 10% | Cuts and breakage |
| Diagonal or herringbone patterns | 15% or more | Many angled cuts |
| Carpet | 5–10% | Roll width and pattern direction |
| Paving slabs | 10% | Cutting around edges and obstacles |
| Turf | 5% | Trimming and settling |
| Patterned wallpaper | 10–15% | Pattern matching between drops |
How to Work Out the Area of a Driveway or a Pitched Roof
Two outdoor jobs catch people out: long, narrow driveways and sloping roofs.
Driveway
Measure the length and the average width. If the drive widens into a turning area, treat it as a separate rectangle. A drive that is 15 m long and 3.2 m wide has 15 × 3.2 = 48 m². Add a 3 m × 3 m turning area (9 m²) and the total is 57 m². If you plan to pour concrete 100 mm (0.1 m) thick, the volume is 57 × 0.1 = 5.7 m³, which you can check with our Concrete Calculator.
Pitched Roof
The roof surface is bigger than the floor beneath it because it slopes. To work out the sloping area, measure the footprint (length × width of the building, including overhangs) and divide by the cosine of the roof pitch angle. Builders use this “pitch factor” to avoid climbing up with a tape measure.
| Roof pitch | Pitch factor (1 ÷ cos) | Roof area for a 60 m² footprint |
|---|---|---|
| 15° | 1.035 | 62.1 m² |
| 20° | 1.064 | 63.9 m² |
| 25° | 1.103 | 66.2 m² |
| 30° | 1.155 | 69.3 m² |
| 35° | 1.221 | 73.2 m² |
| 40° | 1.305 | 78.3 m² |
| 45° | 1.414 | 84.9 m² |
A 10 m × 6 m footprint is 60 m². At a 30° pitch the factor is 1.155, so the roof surface is 60 × 1.155 = 69.3 m². This simple method applies to a plain two-sided pitched roof; hips, dormers and valleys add extra area that needs separate calculations.
Converting Between m², ft² and Other Units
If your plans are in square feet but your supplier sells by the square metre, convert before you order. Remember that area conversions use the square of the length conversion, so you cannot just multiply by 3.28 or by 100.
| To convert | Multiply by | Example |
|---|---|---|
| m² → ft² | 10.764 | 15 m² = 161.5 ft² |
| ft² → m² | 0.0929 | 200 ft² = 18.58 m² |
| m² → cm² | 10,000 | 0.5 m² = 5,000 cm² |
| cm² → m² | 0.0001 | 2,500 cm² = 0.25 m² |
| yd² → m² | 0.8361 | 10 yd² = 8.36 m² |
| hectares → m² | 10,000 | 0.3 ha = 3,000 m² |
| acres → m² | 4,046.86 | 0.25 acre = 1,011.7 m² |
For a broader look at land units and tools, see How to Measure Area.
How to Work Out the Area of Several Rooms or a Whole House
When you need to total several spaces, list each room on its own line with its dimensions and area, then add the column. Decide beforehand whether you are including hallways, stairs, wardrobes and bathrooms, and write it down so that you use the same rules throughout. The full approach, including the difference between gross, net and usable areas, is explained in How to Calculate Area Covered.
| Room | Length × width | Area |
|---|---|---|
| Lounge | 5.4 × 3.9 m | 21.06 m² |
| Kitchen | 4.0 × 3.0 m | 12.00 m² |
| Bedroom 1 | 4.2 × 3.6 m | 15.12 m² |
| Bedroom 2 | 3.3 × 2.9 m | 9.57 m² |
| Bathroom | 2.5 × 2.0 m | 5.00 m² |
| Hallway | 4.5 × 1.2 m | 5.40 m² |
| Total | 68.15 m² |
Common Mistakes When You Work Out Area
- Measuring in different units. Mixing metres and centimetres is the most common error.
- Forgetting to subtract openings when working out wall area for paint.
- Not allowing for waste. Order exactly the calculated amount and you will probably run short.
- Using internal and external measurements together. Decide which one you need and stick to it.
- Rounding down. Always round up when ordering tiles, packs and rolls.
- Assuming the room is square. Measure both pairs of opposite walls.
When you are ready to check your numbers, try the Area Calculator, or move on to volume problems with the Volume Calculator.
Check your room, wall or garden measurements with the free Area Calculator.
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