HOW TO SCALE A 3D MODEL IN YOUR SLICER

Scaling changes the dimensions of the loaded model before slicing. Done correctly, you can resize a part to fit a different application, swap units between metric and imperial, or shrink a print to use less material. Done incorrectly - particularly per-axis scaling on parts with circular features - you get oval holes that don't fit screws and warped geometry that doesn't match the original design intent. The key distinction: uniform scaling preserves proportions; per-axis scaling distorts them. Use per-axis intentionally only.

Use uniform scaling when: the model is the wrong size but the proportions are correct (e.g., a phone holder designed for an iPhone 15 needs to be scaled for an iPhone 15 Pro Max). Use per-axis scaling when: you specifically want to stretch one dimension - a vase taller, a lid wider for a different jar size. Always verify the geometric impact (round becomes oval, square becomes rectangle). Use 2540% scaling when: a model loaded as inches but you're printing in mm (1 inch = 25.4 mm). Flip if the model loaded as mm but should be inches: 0.03937 (1/25.4). Don't scale when: the model has snap-fit features, threaded features, or precise tolerances - those were designed at a specific size and will fail to fit at a different size unless re-engineered.

1. Load the model and check default size. - All slicers display the model's bounding box (X / Y / Z) in mm by default. - If the model is suspiciously small (e.g., 5x5x5 mm) or huge (e.g., 5000x5000), it's likely a unit mismatch. 2. For inch-to-mm conversion: - All slicers: scale tool - enter 2540% as the uniform scale factor. Or scale by 25.4x. - Result: a 1-inch-tall part now displays as ~25.4 mm tall. 3. For mm-to-inch (rare but possible): - Scale by 3.937% or 0.03937x. 4. For uniform proportional resize: - Cura: click the scale icon (handles around the model). Type new value into one dimension - the other two scale proportionally if 'Uniform Scaling' is enabled (default). - PrusaSlicer: scale tool, ensure the chain-link icon is locked, type new dimension or percentage. - OrcaSlicer / Bambu Studio: scale icon, lock the proportions toggle, enter percentage or dimension. 5. For per-axis (intentional distortion): - Disable the 'Uniform' / 'Lock proportions' toggle. - Enter X, Y, or Z value individually. - Verify the resulting geometry in the preview. 6. For exact-mm sizing: - Enter the desired mm value into one dimension (with uniform locked) - the slicer calculates the percentage automatically. 7. After scaling, re-slice and inspect the layer count, print time, and geometry preview. A scaled-up model uses dramatically more time and filament.

Per-axis scaling without realising it. A part with circular holes becomes ovals - won't fit screws or bolts. Always verify the lock-proportions setting. Forgetting unit conversion. A model designed in inches loads as mm in most slicers - displays at 1/25.4 of intended size. Look for tiny models and apply 2540%. Scaling functional parts. Snap fits, threads, and clearances were designed at a specific size. Scaling 110% breaks the design intent. Scaling without re-orienting. A scaled-up model may need different supports or orientation than the original. Re-check. Scaling huge prints without considering print time. A 200% scale = 8x the volume = roughly 8x the print time. Check the slicer's time estimate.

For models too large to fit your bed at desired scale, see how-to-split-large-model. For broken models that won't slice cleanly, see how-to-repair-stl. For choosing layer height after scaling, see how-to-choose-layer-height.