Filament usage is how much plastic the printer actually extrudes for a job — not the solid volume of the CAD model. Infill, walls, top/bottom layers, supports, brim, and purge all change the grams you pay for.
This guide explains how slicers estimate usage, why manual volume maths often disagree, and how to turn grams into material cost in ₹ INR. Pair it with the Filament Cost Calculator. Numbers below are illustrative.
What filament usage means
Usage is the mass (or length) of filament consumed for one print, including intentional extras such as supports and skirt/brim. Selling quotes that use only “model volume × density” usually undercount real jobs.
How slicers estimate consumption
Modern slicers simulate toolpaths: perimeters, infill lattices, solid layers, and support structures. They convert path length and filament cross-section into metres and grams using your diameter and material density settings. Prefer the slicer’s filament estimate when you have sliced the exact profile you will print.
Filament weight vs model volume
A watertight mesh volume (for example from an STL analyzer) is the solid interior of the geometry. Printed parts are rarely solid. Even at 100% infill, slicer paths, extrusion multipliers, and small gaps mean volume × density is only a rough upper bound — never an exact invoice.
Use the STL Viewer & Analyzer to check size and triangle count first; treat any volume figure as approximate and only when the mesh looks closed enough.
How infill affects usage
Infill percentage and pattern dominate gram count on hollowable shapes. Dropping from 40% to 15% can cut a large share of material on boxy parts, while thin shells may barely change. Always re-slice after changing infill — do not scale an old gram estimate by hand.
Walls, top/bottom, supports, and brim
- Walls / perimeters — extra loops add plastic around the outline.
- Top and bottom layers — solid skins can outweigh sparse infill on flat parts.
- Supports — often a large hidden cost; include them in usage if you print them.
- Brim / skirt / purge — small per job, but matter for short multicolor or tool-change runs.
Density and material differences
Slicers convert volume of extruded filament using density (g/cm³). Typical starting points many slicers ship with: PLA ~1.24, PETG ~1.27, ABS ~1.04 — but brand datasheets vary. Wrong density skews grams even when path length is right. Prefer manufacturer density when you care about cost accuracy.
Cost per gram and material cost
- Filament cost per gram = spool price ÷ usable spool weight in grams
- Material cost = estimated filament grams × cost per gram
Use net filament weight on the spool, not the boxed gross weight that includes the empty spool. See also the short filament cost primer.
Worked example (illustrative)
- Spool: ₹1,200 for 1,000 g net → ₹1.20/g
- Slicer estimate for the job (with supports): 84 g
- Raw material cost: 84 × 1.20 = ₹100.80
A solid-volume shortcut that ignored 20% infill might have guessed far fewer grams and underpriced the job. Enter 84 g in the Filament Cost Calculator to match this example, then pass ₹100.80 into the Print Cost Calculator if you need electricity and markup.
Why manual estimates differ from the slicer
- Manual maths often assume 100% solid fill
- Density or diameter settings differ from the spool
- Supports, brim, and purge were omitted
- Flow / extrusion multiplier is not 100%
- Units mix-ups (cm vs mm) on imported STLs