To preserve proportions, apply one factor to all three dimensions. Divide the target dimension by the current dimension on your chosen axis. The scaling calculator provides the factor, final percentage and resulting dimensions; it does not modify your file.
Check the model before calculating
Record X, Y and Z as displayed by the slicer, in mm, and the model’s orientation. Rotation can change its bounding box. Choose a reference dimension that actually matches your objective: total height, external width or another known dimension.
If your target is an internal hole dimension, total model width does not determine it. Use the actual internal dimension in your design software; do not invent a correspondence between different dimensions.
Calculate one factor
For current dimension a and target b, factor k = b / a. The results are X × k, Y × k and Z × k. Final percentage is 100 × k; relative change is 100 × (k − 1).
Theoretical example: a 100 × 50 × 20 mm model must measure 160 mm on X. The factor is 160 / 100 = 1.6. The result is 160 × 80 × 32 mm, or 160% of the original size and an increase of 60%.
| Target X, originally 100 mm | Factor | Final percentage | Change |
|---|---|---|---|
| 160 mm | 1.6 | 160% | +60% |
| 75 mm | 0.75 | 75% | −25% |
| 25 mm | 0.25 | 25% | −75% |
“Reduce by 25%” means retain 75%; “scale to 25%” means reduce by 75%. This distinction prevents a command error unrelated to the printer.
Apply the scale in the slicer
The cited PrusaSlicer documentation distinguishes uniform scaling using corner handles from changing a single axis. Controls may differ by version. Prefer numerical fields and proportion locking when available, then check all three displayed dimensions.
- Keep a copy of the original model.
- Check its units and orientation.
- Choose uniform scaling.
- Enter the factor or percentage according to the software field.
- Read X, Y and Z again and compare them with the calculation.
- Slice again and inspect the result, not only the silhouette.
Do not multiply cost by the linear factor
In ideal, fully solid geometry, lengths follow k, areas k² and volume k³. At k = 1.6, the volume ratio would be 4.096. This theoretical result is not an FDM consumption multiplier: the slicer rebuilds walls, infill and supports. Recalculate its estimates after the change.
Distinguish a numerical target from the final part
Reaching a dimension in the slicer does not prove the printed object will match it exactly. Model and printed-part dimensions explain the difference. For a mechanical fit, prepare checks of functional dimensions; do not correct the entire model from one local defect.
Sources consulted
- Move, Rotate, Scale tools — Prusa Research
Accessed