Filament Length to Weight Calculator
Turn a length of filament into grams. Handy for costing a print from its sliced length, or checking how much of a spool a model will use — just pick your material and diameter.
Density varies by brand and colour — check your spool's spec sheet and adjust if you need an exact figure.
Formula & how it works
The strand is a cylinder. Cross-sectional area is π × (diameter ÷ 2)² in square millimetres. Multiplied by the length in metres it gives volume in cubic centimetres, since a square-millimetre times a metre is exactly one cubic centimetre.
Weight is then area × length × density, with density in grams per cubic centimetre.
Worked example
Standard 1.75 mm PLA has a cross-section of about 2.41 mm², so at a density of 1.24 g/cm³ each metre weighs roughly 2.98 grams. A 330-metre length therefore comes out near 984 grams — just about a full 1 kg spool, which is why that length is a common spec.
Using the result
Costing from sliced length
Some slicers and older tools report a print in length rather than weight. Converting to grams lets you price the material against a spool's cost per kilogram, which is how filament is sold. Pair it with the cost calculator once you have the weight to fold in machine time and failures.
Diameter matters more than it looks
Because area depends on the square of the diameter, moving from 1.75 mm to 2.85 mm nearly triples the weight per metre. Always set the diameter to your actual filament, and if you print with unusually tight or loose tolerances, a fraction of a millimetre will shift the total.
Match density to the material
The presets are typical values, but colour, fillers, and additives change density. Glow, metallic, wood, and carbon-fibre blends run heavier than plain PLA. For a precise figure, use the density on your spool's data sheet rather than the default.