PLA Filament by Volume and Density

How much PLA filament a 3D print really uses

Once you know the part volume and the polymer density, the PLA mass falls right out: m = V · ρ, where standard PLA sits at ρ ≈ 1.24 g/cm³. To turn that into a length of 1.75 mm filament you divide by the cross-section, L = V / (π · (d/2)²). That math is why a 1 kg spool of 1.75 mm PLA gives you around 330 m of filament, and only about 110 m once you step up to 2.85 mm.

Take a run-of-the-mill desktop print, say a 5×5×5 cm part at 20% infill with 3 perimeters and 0.2 mm layers. It extrudes maybe 25 cm³, which works out to about 30 g of PLA, or roughly 3% of a 1 kg spool. The same density math applies whether you run a Creality Ender 3, a Prusa MK3/MK4, a Bambu Lab A1 or a Voron. PLA itself is biodegradable, but only under industrial composting, and it comes from corn starch or sugarcane.

Applications

Quote a batch of parts by multiplying mass by price per kg and adding machine time. Work out how many prototypes will fit on the spool you already have. Compare PLA at 1.24 g/cm³ against PETG (1.27), ABS (1.04), ASA (1.07), TPU (1.21) or Nylon (1.13–1.15). Plan ahead for spool swaps on the long multi-day jobs. Your slicer already reports mass and length, sure, but having the formula in hand means you can double-check what it tells you, or get a cost figure before you even import the STL.

FAQ

Why doesn’t my spool weigh exactly 1 kg? Because the number on the label counts the filament alone. The plastic or cardboard reel it’s wound on adds another 150–250 g, so weigh the empty spool if you plan to reuse it for refill rolls.

Does infill change the formula? It does, in the sense that V means the volume you actually extrude, not the bounding box. A solid 100 cm³ cube burns 124 g, whereas the same cube printed with 20% gyroid infill and 3 perimeters comes in closer to 35–45 g.

Is PLA really biodegradable? Only in an industrial composter, at roughly 58 °C with controlled humidity. Toss it in a backyard pile or a landfill and it’ll stick around for decades. Most recycling streams turn PLA away anyway, since it contaminates PET.