Start from the current model size
The model scale and fit calculator uses the current bounding dimensions, not a drawing’s advertised nominal size. Confirm the imported model’s units and X, Y and Z dimensions in the slicer before entering them.
A uniform scale changes all dimensions together. Increasing X from 100 to 150 mm makes a 60 mm Y dimension become 90 mm and a 40 mm Z dimension become 60 mm. It does not independently stretch one axis or preserve an original wall thickness.
Treat scale ratios as ratios
Changing 1:72 to 1:48 means the model becomes larger: the factor is 72/48, or 150%. Reversing those numbers would shrink it. The tool states the resulting dimensions so the ratio can be checked against an intuitive physical size.
A percentage is dimensionless. Selecting inches instead of millimetres changes the shown lengths, not the physical scale factor.
Understand the orientation search
Fixed orientation compares X with printer X, Y with printer Y and Z with printer Z. Allowing 90-degree permutations tests six axis assignments. It does not search every possible tilted position, arrange multiple objects or judge whether one orientation prints well.
Clearance is deducted at both ends of each axis, including Z. This is a conservative bounding-space convention. It is not automatic placement on the build plate, and it does not include a generated support envelope.
Finish the check in the slicer
A rectangular printer volume cannot represent a circular bed or every keep-out zone. Clips, a brim, supports and print-head motion can consume space outside the part’s simple box. Review the scaled model and generated toolpaths in the actual printer profile before starting.
After selecting a size, obtain the new slicer mass and duration for a printing cost estimate. A bounding-box scale alone cannot reliably predict either one, particularly if supports or wall-count behavior changes.