Filament Length to Weight Calculator

In short Filament is a cylinder, so converting between the length a slicer reports and the weight a scale measures is geometry plus one density. A metre of 1.75 mm filament is 2,405 mm³, and at the 1.24 g/cm³ typical of PLA that is 2.98 g — which is why a 1 kg spool of PLA holds roughly 335 metres. The number worth carrying away is what happens when the diameter changes, because diameter enters as a SQUARE. 2.85 mm filament is not 1.63 times heavier per metre than 1.75 mm, it is 2.65 times heavier, and the same weight of it is 2.65 times shorter. That ratio is exact and it holds for every material, because the density cancels out of the comparison entirely — which is also how this tool is tested. Density is the one figure here that is not geometry, and it varies: PLA and PETG sit near 1.24 and 1.27, ABS nearer 1.04, and filled filaments wander a long way from all of those because the filler is not plastic. Wood-filled and carbon-filled spools are the ones where a table will let you down. If your spool prints a density, type it in — it is true for your spool in a way no typical value can be. And remember this is nominal geometry: real filament varies by a few hundredths of a millimetre along its length, which is exactly what the tolerance figure on a good spool is telling you.