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Square metres are the standard unit for measuring floor space, walls, land and materials. Whether you're buying flooring, estimating paint, or sizing a room, it starts with one simple calculation: width times length. The tool takes your two measurements in metres and returns the area in square metres instantly.
Enter the width and length, and the area in m² appears at once.
Square Meter Calculator: step-by-step worked example
The floor of a 4 m × 5 m room
- Width (m)
- 4
- Length (m)
- 5
- 1
Area
Area = Width × Length
4 × 5 = 20 m²
- 2
In square feet
1 ft = 0.3048 m → 1 ft² = 0.09290304 m²; ft² = m² ÷ 0.09290304
20 ÷ 0.09290304 = 215.2782 ft²
- 3
Perimeter (for skirting)
Perimeter = 2 × (Width + Length)
2 × (4 + 5) = 18 m
- 4
Flooring with 10% waste
Material = Area × 1.10
20 × 1.1 = 22 m²
- Net area20 m²90.9%
- 10% waste2 m²9.1%
Good to know: Listed (gross) floor area includes walls and shared space; room-by-room net area is smaller. Allow 5–10% extra flooring for straight laying and about 15% for diagonal.
Square Meter Calculator — how it works
The calculation
Area (m²) = width (m) × length (m). A room 4 m wide and 5 m long is 4 × 5 = 20 m².
Keep units consistent
Both measurements must be in metres. If you measured in centimetres, divide by 100 first (350 cm = 3.5 m). Mixing units gives a wrong result.
Practical uses
- Flooring: multiply the room area by the tile or laminate price per m², and add about 10% for waste and cuts.
- Paint: find the wall area (wall length × height), subtract doors and windows, and divide by the paint's coverage per m².
- Land and gardens: for a rectangular plot, width × length; for irregular shapes, split into rectangles and add.
Irregular rooms
For an L-shaped or irregular room, divide it into rectangles, calculate each area, and add them together. For non-rectangular shapes (triangles, circles), an area calculator has the right formulas.
Worked example
A room 4 m wide and 5 m long has an area of 4 × 5 = 20 m². If you're laying laminate priced per square metre, you'd multiply 20 m² by the price and add about 10% for waste — so you'd buy for roughly 22 m². If one measurement was taken in centimetres (say 450 cm long), convert it first: 450 cm = 4.5 m, giving 4 × 4.5 = 18 m². Keeping both measurements in metres is what keeps the result correct.
Square metres by width and length
| Dimensions | Area |
|---|---|
| 3 m × 4 m | 12 m² |
| 3.5 m × 4.5 m | 15.75 m² |
| 4 m × 5 m | 20 m² |
| 4 m × 6 m | 24 m² |
| 5 m × 6 m | 30 m² |
| 5 m × 8 m | 40 m² |
| 6 m × 8 m | 48 m² |
| 8 m × 10 m | 80 m² |
| 10 m × 10 m | 100 m² |
| 10 m × 15 m | 150 m² |
| 12 m × 20 m | 240 m² |
| 20 m × 25 m | 500 m² |
Measured in centimetres? Divide by 100 first: 350 cm × 450 cm = 3.5 m × 4.5 m = 15.75 m².
Frequently asked questions
How do I calculate square metres?+
Multiply the width by the length, both in metres: a 4 m × 5 m room is 20 m². Just enter the two measurements in metres.
How do I convert centimetres to metres first?+
Divide by 100: 350 cm = 3.5 m. Both measurements must be in metres before multiplying, or the result will be wrong.
How much flooring do I need for a room?+
Find the room area (width × length), then add about 10% for waste and cuts. For a 20 m² room, buy for roughly 22 m² of flooring.
How do I calculate the area of an irregular room?+
Split it into rectangles, find each area, and add them. For triangular or circular sections, an area calculator has the appropriate formulas.
How do I work out paint quantity from square metres?+
Calculate the wall area (length × height), subtract doors and windows, then divide by the paint's coverage per m² (on the tin). Add a second coat if needed.
How many square feet is a square metre?+
1 square metre ≈ 10.76 square feet. To convert m² to sq ft multiply by 10.76; a 20 m² room is about 215 sq ft.
About this page
- Publisher:
- Kalkoro — Teknolojig Bilişim Teknolojileri A.Ş., İstanbul
- Written by:
- Ahmet Tur — Editor (Math, date & time, unit conversion, physics & chemistry, everyday tools)
- Reviewed by:
- Kübra Yıldız — Editor
Parameters come from official sources; the last update date is shown at the bottom of the page.
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