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What this tool does
Filament is sold by weight and used by length, and every 3D printer owner eventually needs to cross from one to the other. This filament length weight converter turns grams into metres and metres into grams for the common filament diameters, 1.75 mm and 2.85 mm, and for six materials: PLA, PETG, ABS, TPU, ASA, and nylon. Pick a direction, a diameter, and a material, enter an amount, and the tool gives the converted figure, with the cross-section and density shown so you can check the working.
The tool runs in your browser and needs no account. It is handy in three everyday moments: judging whether a spool holds enough for a print, weighing a half-used spool to guess what is left, and comparing spool prices fairly, because a heavier spool is not always a longer one.
The formula, in plain words
A length of filament is a long, thin cylinder. Its volume is its cross-section area times its length, and its weight is that volume times the material’s density. For 1.75 mm filament the cross-section is about 2.41 square millimetres. So 100 grams of PLA, at a density of 1.24 grams per cubic centimetre, is about 80,645 cubic millimetres of plastic, which stretches to roughly 33.5 metres. The same 100 grams of PETG, which is denser at 1.27, stretches slightly less, about 32.7 metres. Density is the whole reason the material setting matters.
Diameter matters even more, because area grows with the square of the diameter. A 2.85 mm filament has about 2.65 times the cross-section of a 1.75 mm one, so 100 grams of 2.85 mm PLA is only about 12.6 metres. That is why printers that use 2.85 mm filament chew through spools by weight so much faster, and why a gram-based price comparison across diameters is misleading without conversion.
A worked example
Say your slicer reports a print needs 24 metres of 1.75 mm PLA. Converted, that is about 71.6 grams, because each metre of 1.75 mm PLA weighs roughly 2.98 grams. If your spool holds 300 grams, the print uses under a quarter of it, and you could print it four times over. Now flip the direction: a spool with 150 grams left holds about 50.3 metres of the same filament, which is enough for two prints of 24 metres with a little to spare, but not three.
Try the same numbers for ABS, at 1.04 grams per cubic centimetre. One hundred grams stretches to about 40 metres, because ABS is lighter for its volume. A print that weighs 71.6 grams in PLA would weigh only about 60 grams in ABS for the same volume, which is one reason slicer weight estimates change when you switch materials, even for the identical model.
Measuring what you actually have
The converter is exact arithmetic, but its inputs are only as good as your measurements. Weigh the spool with kitchen scales, then subtract the empty spool weight, which the maker usually prints on the spool or the box. If you do not know it, weigh an identical empty spool, or use the companion spool remaining calculator, which walks through the same subtraction. Do not guess the empty weight: a 250 gram spool error on a half-used kilogram spool throws the length estimate off by about 84 metres of 1.75 mm PLA.
Also check the real diameter. Filament labelled 1.75 mm often measures 1.72 to 1.78 mm, and since area depends on the square of the diameter, a 0.03 mm error shifts the length by about 3.5 percent. For casual planning that is fine. For a print that must fit on the last of a spool, measure the filament in several places with calipers and use the average.
Limits to keep in mind
Density values here are typical figures for each material, not guarantees. Filled filaments change the picture sharply: wood-filled, carbon-filled, and metal-filled filaments are denser than their base plastic, sometimes by 20 percent or more, so this converter will overestimate their length. Glow-in-the-dark and silk filaments also differ slightly. If you print with a filled filament, find the maker’s stated density and treat the converter’s result as a rough guide.
Finally, remember that the converter counts the filament itself, not the print. Skirts, brims, supports, and purged material all consume filament that the model volume does not include, and failed prints consume it twice. When a spool is nearly empty, add at least ten percent to the slicer’s estimate before deciding the print will fit. This is an educational estimator, and your printer manual and filament maker’s guidance always govern temperatures, materials, and safety.
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