How to calculate film weight from thickness and density

One formula powers film weight, yield and line output. Get it right once and the rest follow.

The formula

Mass = width × thickness × length × density. Keep everything in SI units — metres and kg/m³ — and the answer is in kilograms. The classic mistake is thickness: film is quoted in microns, and 1 micron = 0.000001 m, so 50 µm = 0.00005 m. Density is the resin's, e.g. HDPE ≈ 955, LDPE ≈ 920, PP ≈ 905, PET ≈ 1380 kg/m³.

Worked example

A 1 m wide, 50 µm HDPE film, 500 m long: 1 × 0.00005 × 500 × 955 ≈ 23.9 kg. Per m² at that gauge it is thickness × density = 0.00005 × 955 ≈ 47.75 g/m² (its "GSM").

The three tools it drives

Rearrange the same formula and you get the whole family: the film weight calculator (dimensions → kg), the film yield calculator (kg → metres and m²), and the film output calculator (line speed → kg/hour). For multilayer film, calculate each layer’s mass from its own thickness and density, then add the layer masses. An unqualified average density can give the wrong result.