Linear Metres to Square Metres

How the linear to square metres calculator works

Carpet, sheet vinyl, damp-proof membrane, landscape fabric, roofing felt and artificial grass are all cut from a roll and sold by length, but the job is measured in area. Converting one to the other needs a single extra number: the width. Area equals length times width, so the calculator multiplies the two and gives the result in square metres, square feet and, with US units, square yards.

In metric units the length is in metres and the width in millimetres, so A = L × w ÷ 1000 gives square metres: 10 m of 1000 mm material covers 10 m². In US units the length is in feet and the width in inches, so A = L × w ÷ 12 gives square feet, and dividing by 9 gives square yards: 30 ft of 36 in material covers 90 ft², which is 10 yd². Nothing is estimated. The result is exact for the numbers you enter.

Why "linear metre" means nothing without the width

A linear metre is just a metre of length, whatever the width. Ten linear metres of 4 m carpet covers 40 m²; ten linear metres of 1 m membrane covers 10 m². Suppliers quote in linear metres because that is how they cut the roll, so always ask for the width with the price.

Use the width the material actually covers, not the width of the roll, when the sheets overlap. A 1 m roll laid with 100 mm laps covers 900 mm per run, so 10 m of it covers 9 m², not 10. The same goes for felt and membranes laid with side laps, and for fabrics with a selvedge that is trimmed off.

Exact conversion factors

Metric and US units are tied together by exact definitions. The US National Institute of Standards and Technology sets out the 1959 agreement that makes 1 inch exactly 25.4 mm, and so 1 foot exactly 0.3048 m. From those, its table of conversion factors gives 1 square foot as 0.09290304 m² and 1 square yard as 0.8361274 m². Going the other way, 1 m² is about 10.7639 ft². The calculator uses the exact figures, so 1,000 m² comes out as 10,763.91 ft², not the 10,763.90 a rounded factor would give.

One legacy unit is worth knowing about if you work from old US survey plans. NIST has retired the US survey foot, which differed from the international foot by about two parts in a million; since the start of 2023 it should be avoided except for historic and legacy data. The difference is far too small to matter on a roll of carpet. Both systems are defined from the metre, the SI unit of length maintained by the BIPM.

Working backwards to a length

Often the question runs the other way: how much roll do I need for this area? Divide the area by the width. The calculator shows the length per square metre (or per square foot) for the width you enter, so you can multiply it by the area. A 4 m wide carpet needs 0.25 m of length per m², so a 20 m² room needs 5 linear metres. A 2 m wide vinyl needs 0.5 m per m², so the same room needs 10 m.

That is the net figure. Rooms are rarely an exact multiple of the roll width, patterns have to line up, and seams take a little extra, so the length you order is usually more. Plan the cuts on a sketch before buying.

Worked examples

A path is lined with 25 m of 1.5 m wide landscape fabric: 25 × 1500 ÷ 1000 = 37.5 m², or 403.65 ft². A 3.2 m cut from a 4 m carpet roll covers 12.8 m² (137.78 ft²). In US units, 50 ft of 48 in underlayment covers 200 ft², which is 22.22 yd² or 18.581 m². A 15 ft length of 12 ft wide vinyl covers 180 ft², exactly 20 yd².

Before you order

The conversion is exact; the order is not. Add your own allowance for seams, pattern repeat, laps and offcuts to the area or length, write down the unit the supplier is quoting (linear metres, square metres or square yards) next to your figure, and check the price is for the same unit before comparing quotes.

Watch for three different units on the same material. A UK supplier may price carpet per square metre and cut it by the linear metre, and a US store may show the same product per square foot on the shelf and per square yard on the invoice. A price of £20 per m² on a 4 m roll is £80 per linear metre; $2.50 per ft² is $22.50 per yd². Converting both quotes to one unit is the only fair comparison.

Using this calculator with other BuildMetricLab tools

The carpet and vinyl flooring calculators plan whole rooms, including seams and offcuts, and the feet-and-inches converter handles lengths on their own. All BuildMetricLab tools run in your browser with no sign-up, and every formula is shown on the page so the maths can be checked.