Filament length to weight
Quick answer
One metre of 1.75 mm PLA weighs about 2.98 g, so a one kilogram spool holds roughly 335 metres. Multiply the cross sectional area by the length to get volume, then multiply by density.
Pure geometry and published density. Nothing here is a rule of thumb.
Filament by the spool
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Common questions
How many metres are on a one kilogram spool?
For 1.75 mm PLA it is about 335 metres, and for PETG about 327 metres because PETG is slightly denser. For 2.85 mm filament the same kilogram gives roughly 126 metres of PLA, since the thicker strand holds far more material per metre. Set the calculator to your diameter and material for the exact figure.
Why does my spool weigh more than a kilogram?
The advertised weight is the filament only, and the empty spool adds anywhere from 130 g for a light cardboard core to over 250 g for a moulded plastic one. Weigh an empty spool of the same brand once and keep the number, then you can weigh a part used spool and know what is left.
Can I use this to work out how much filament is left?
Yes, and it is the most reliable way short of a scale. Weigh the spool, subtract the known empty spool weight, and that is the filament mass remaining. Divide by the grams per metre figure this calculator gives you to get the remaining length.
Does filament diameter vary enough to matter?
Good filament holds 1.75 mm plus or minus 0.02 mm, which changes the volume by roughly two percent at the extremes. That is small for cost purposes but it is exactly why your slicer has a filament diameter setting, because a consistent error there shows up as persistent over or under extrusion.