FDM Filament Calculator

This calculator splits a part's bounding volume into two zones — the solid outer shell and the interior fill — because FDM printers deposit them differently. It approximates the shell's share of total volume as shell thickness divided by a rough 20mm average wall-to-center distance, then applies your chosen infill percentage only to what's left over (the interior). Add those two fractions together and you get the "effective fill" — the real percentage of the part's volume that actually gets filled with plastic, which is always higher than your raw infill setting because the solid shell counts too. From there the math is straightforward: multiply part volume by effective fill to get material volume, multiply by density to get weight, and back out filament length by treating the filament as a cylinder (volume = πr²·length) using the diameter you specify.

The spool-used percentage just compares that weight against your spool's net weight. The one figure to watch is estimated cost: it's always computed at a flat $25/kg PLA rate, so if you're printing ABS, PETG, nylon, or TPU — materials this calculator already lets you set a different density for — the dollar estimate will be off from what you actually pay, since real filament pricing varies significantly by material and brand. Treat the cost output as a ballpark for standard PLA and use your own per-kilogram price for anything else. Also remember the 20mm shell-zone assumption is a simplification: very thin-walled or unusually shaped parts will see more error in the shell/infill split than a typical blocky print.