How to Calculate Roofing Felt Weight per Square Metre

The calculation

To calculate average mass per square metre, divide roll mass by nominal sheet area. Sheet area is roll width multiplied by roll length. Keep the units consistent: kilograms divided by square metres gives kilograms per square metre.

For a nominal 1 m × 20 m roll weighing 20 kg on the agreed product-mass basis, the calculation is 20 ÷ 20 = 1 kg/m², or 1,000 g/m². For a 1 m × 8 m roll at 7 kg, the result is 7 ÷ 8 = 0.875 kg/m², or 875 g/m².

Choose a consistent weight basis

The examples are arithmetic comparisons. Their usefulness depends on what is included in the measured roll mass. If wrapping or the core is included in one measurement but excluded from another, the calculated figures are not on the same basis.

Before comparing suppliers, agree whether you are using net product mass or finished-roll gross mass. Record width and length as well, because a different measured sheet area changes the result.

What this number does and does not tell you

Mass per area helps compare roll formats and check the consistency of an agreed order. It does not by itself identify the paper grade, asphalt treatment, coating distribution or installation suitability.

Use it alongside the material description, surface, sample approval and order specification. Do not convert a calculated mass per area into an unsupported certification or performance claim.

Use the result in your buying documents

A useful comparison table includes width, length, product mass, gross mass and calculated mass per area. State the weight basis beside the calculation so colleagues understand how the figure was produced.

Merily can discuss the available roll combinations against your target dimensions and mass. Include the specification you currently sell, your order quantity and destination when requesting a bulk quotation.

Worked arithmetic examples