What this calculator does
Most 3D prints are not solid all the way through: a solid outer shell wraps a mostly hollow interior filled with a repeating infill pattern at a chosen density. The effective volume of filament used is the full shell volume plus only a fraction of the interior volume, set by the infill percentage.
This is the calculation a slicer performs automatically when it reports a print’s estimated weight, but working through it directly is useful for understanding how much of a model’s bulk is actually structural shell versus adjustable infill, and how much weight (and filament) a lower infill percentage would actually save.
The formula
Add the shell volume to the interior volume multiplied by the infill percentage (divided by 100) to get the effective print volume. Multiply that by the filament density to get weight.
| Term | Meaning |
|---|---|
| Shell volume | The volume of the solid outer walls and top/bottom layers, printed at 100% regardless of infill setting. |
| Interior volume | The remaining internal volume of the model, of which only the infill percentage is actually filled with plastic. |
| Infill percentage | The fraction of the interior volume that is filled with the infill pattern, rather than left hollow. |
The inputs explained
| Field | What to enter |
|---|---|
| Shell (perimeter/wall) volume (cm³) | The volume taken up by the outer walls and top/bottom solid layers. Estimate this from wall count and thickness, or from a slicer’s 100%-infill preview. |
| Interior volume (total model volume minus shell) (cm³) | The model’s total volume minus the shell volume: the space the infill pattern occupies at less than 100%. |
| Infill percentage (%) | The infill density percentage set in the slicer. |
| Filament type | The loaded filament material, to convert the effective volume into a weight. |
When to use it
Deciding whether a lower infill is worth it
Because only the interior volume scales with infill percentage, and shell volume never changes, this shows exactly how much weight is actually saved by dropping from, say, 40% to 15% infill.
Estimating weight before adjusting infill in the slicer
Working out the effective volume at a candidate infill percentage gives a weight estimate without needing to re-slice the model at every setting to check.
Understanding why thin-walled models barely change with infill
A model that is mostly shell, with very little interior volume, shows only a small weight change across a wide range of infill percentages, since there is little interior left to fill in the first place.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How effective print volume changes with infill percentage
A fixed shell and interior volume, across a range of infill percentages.
| Infill percentage | Effective print volume | Estimated weight |
|---|---|---|
| 0% | 8.00 cm³ | 9.9 g |
| 10% | 11.20 cm³ | 13.9 g |
| 20% | 14.40 cm³ | 17.9 g |
| 40% | 20.80 cm³ | 25.8 g |
| 60% | 27.20 cm³ | 33.7 g |
| 100% | 40.00 cm³ | 49.6 g |
Questions
How do I find the shell and interior volumes for my model?
Some slicers show a 0%-infill preview (shell volume alone) and a 100%-infill preview (total model volume) separately; subtracting the two gives the interior volume. Otherwise, wall count multiplied by wall thickness and surface area gives a reasonable shell estimate.
Does infill percentage affect strength in direct proportion?
No, not linearly. Strength gains from higher infill percentages taper off well before 100%, which is why most functional prints use a moderate infill (commonly 15 to 30%) rather than a solid fill, trading some strength for a large saving in material and time.
Why does the shell volume not change with infill percentage?
The shell (outer walls and top/bottom solid layers) is printed at full density regardless of the infill setting, since it defines the visible surface and the structural boundary of the part; only the hidden interior varies with infill.
Can I use this to estimate print time as well as volume?
Not directly. Infill patterns print at different speeds and with different amounts of travel than solid shells, so time does not scale with volume in quite the same simple way; the print time estimate calculator works from filament length instead.
To turn this effective volume into a cost, use the filament weight and cost calculator. For how many solid layers make up the shell itself, see the layer count calculator.