Square Meter Calculator
Calculate square meters (m^2) by entering length and width in meters. Fast and clear result for floors, rooms, and walls.
Square metres in practice: rooms, materials, and property
Calculating square metres is easy. Knowing which square metres to count is not - property listings, tiling quotes, and flooring orders each use a different definition of the same room, and the gap between them can be 20% or more.
Formula
m^2 = length (m) x width (m)
Convert every measurement to metres before multiplying. 250 cm becomes 2.5 m, not 250.
Three different "floor areas" for the same room
Property measurement standards disagree deliberately, because they serve different purposes. Knowing which one a figure refers to matters when comparing listings.
- Gross external area (GEA): measured to the outside face of external walls. Used for planning applications and construction costing.
- Gross internal area (GIA): measured to the inside face of external walls, including internal partitions. Used for residential valuation in much of the UK.
- Net internal area (NIA), also called usable or carpet area: excludes walls, columns, stairwells, and lift shafts. Used for commercial leases and for what you can actually furnish.
- The gap between GIA and NIA in a typical apartment is 10 to 20%, which is why a listed "85 m^2" flat can feel like 70.
Ordering materials: the allowances that matter
Never order exactly the calculated area. Every material has a characteristic wastage rate driven by how it is cut and laid.
- Ceramic and porcelain tiles: 10% straight lay, 15% diagonal, 20% for mosaic or complex patterns.
- Laminate and engineered wood: 5 to 8% in simple rooms, 15% for herringbone.
- Carpet: sold in fixed roll widths, usually 4 m or 5 m, so the practical wastage depends on room width rather than area.
- Paint: coverage is typically 10 to 12 m^2 per litre per coat on smooth surfaces, but half that on bare plaster or textured walls.
- Turf and paving: 5% for rectangular areas, 10% or more where curves are involved.
Squaring the conversion factor
Area conversion is where most numerical errors occur, because the linear factor must be squared.
A square metre is 10.7639 square feet, not 3.2808. A hectare is 10,000 m^2 and an acre is 4,046.86 m^2, so a hectare is about 2.47 acres. A "square" in Australian and US construction is 100 square feet, or 9.29 m^2.
When converting a room quoted in feet and inches, convert each dimension to metres first, then multiply. Converting the area afterwards works too, but converting mid-calculation is where the factor gets applied once instead of twice.
Worked example
A bathroom measures 2.4 m by 3.1 m, with a shower tray 0.9 m by 0.9 m and a bath 1.7 m by 0.7 m occupying floor space.
Gross floor: 2.4 x 3.1 = 7.44 m^2. Subtracting the shower tray (0.81 m^2) and bath (1.19 m^2) leaves 5.44 m^2 to be tiled.
At 10% wastage for a straight lay that is 5.98 m^2. Tiles sold in boxes covering 1.2 m^2 mean 5 boxes, giving 6.0 m^2 - just enough, with almost no margin for breakage. Ordering 6 boxes is the sensible call.
Square metre equivalents
| Unit | In square metres | Note |
|---|---|---|
| 1 square foot | 0.092903 | Exact by definition |
| 1 square yard | 0.836127 | Common for carpet |
| 1 square (construction) | 9.2903 | 100 square feet |
| 1 are | 100 | Rare outside agriculture |
| 1 dunam | 1,000 | Turkey, Israel, Balkans |
| 1 acre | 4,046.86 | 43,560 square feet |
| 1 hectare | 10,000 | 2.471 acres |
Frequently Asked Questions
Related calculators
References
- RICS Property Measurement / IPMS standards
- NIST Special Publication 811 - Guide for the Use of the SI
Last reviewed: 2026-08-07. This page is informational. For legal, medical, tax, or financial decisions, confirm the result with a qualified professional.