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Why infill weight matters before you print
Most people choose infill percentage by habit: twenty percent for display pieces, forty for functional parts, one hundred for things that must not break. Few people know what that choice costs in filament. The difference between twenty and forty percent infill on a large model can be hundreds of grams, which is real money, real print time, and real weight in the finished part. This calculator isolates the infill alone, so you can see the cost of that one setting before you commit to a long print.
The math is straightforward. The infill volume is the model volume multiplied by the infill percentage. A 100 cubic centimetre model at twenty percent infill contains 20 cubic centimetres of infill plastic. Multiply by the material density to get weight: PLA at 1.24 grams per cubic centimetre gives 24.8 grams of infill. The calculator also converts that weight into metres of 1.75 mm filament, so you can check whether the spool you have left is enough for the job.
How to find your model volume
Your slicer shows the model volume, or you can estimate it from the slicer’s filament estimate for a solid print. Some slicers report volume directly in the print summary; others report only weight and length, from which volume follows by dividing weight by density. If you are working from a model file alone, free mesh tools report volume for any closed mesh. The number does not need to be perfect for comparison purposes: the same volume error applies to every infill setting you compare, so the ranking stays honest even if the absolute weight is slightly off.
Note what this calculator deliberately leaves out. Walls, top and bottom solid layers, and supports are not infill, and on many models they outweigh the infill itself. A small model with thick walls may use more plastic in its walls than in its infill at any percentage. Use this tool to compare infill choices, and use your slicer’s full estimate for total cost. Confusing the two is the one mistake that makes people think the calculator is wrong.
A worked example
Consider a bracket with a volume of 200 cubic centimetres, printed in PETG at 1.27 grams per cubic centimetre. At fifteen percent infill, the infill volume is 30 cubic centimetres and the weight is 38.1 grams. At fifty percent infill, the volume is 100 cubic centimetres and the weight is 127 grams. The jump from fifteen to fifty percent costs about 89 grams of filament for this one part, which is roughly a tenth of a kilogram spool. If you print ten brackets, the choice costs nearly a kilogram.
Now consider the strength side of the same choice. For most brackets, the jump from fifteen to fifty percent infill adds far less strength than adding one extra wall perimeter, because walls carry most of the load in a printed part. That is why experienced printers raise wall count before infill percentage when a part needs strength. The calculator lets you price the infill decision honestly, and then you can judge whether the extra grams buy enough strength to be worth it.
Choosing an infill percentage
Display pieces that carry no load print well at ten to fifteen percent infill, especially with a pattern like gyroid that supports top layers evenly. Everyday functional parts, such as brackets, hooks, and mounts, suit twenty to thirty percent. Parts that take repeated impact or heavy load may justify forty to sixty percent, but above sixty percent the returns shrink fast while weight and time keep climbing. One hundred percent infill is rarely the strongest choice per gram: it prints slowly, traps heat, and can warp, while a well-designed part with thick walls and moderate infill is often stronger in practice.
Pattern matters too. Gyroid and cubic patterns give even strength in all directions, while grid and lines are strong in one direction and weak in another. If your part is loaded from one known direction, a directional pattern aligned with the load can beat a higher percentage of the wrong pattern. The calculator does not model pattern, so treat its weight as a volume-based estimate: real patterns leave small air gaps that the simple volume math does not capture, and the difference is usually a few percent.
Frequently asked questions
Why does my slicer show more filament than this calculator? Because the slicer counts walls, solid layers, and supports as well. This tool counts infill only, by design.
Does infill percentage affect print time much? Yes, roughly in proportion to the infill volume, though travel moves and wall time stay constant. Doubling infill rarely doubles total time, but it always adds time.
Can I use this for 2.85 mm filament? The weight figure works for any diameter, since it comes from volume and density. Only the metres figure assumes 1.75 mm filament, so ignore that line for thicker filament.
These figures are estimates and general guidance only, not a guaranteed print result. Your filament manufacturer’s datasheet and your printer’s own calibration govern every setting. Use the calculator above to price your infill choice, then check the slicer’s full estimate for the total.
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