Resize an STL File

Use the STL Editor to scale an STL in your browser without uploading it. Calculate the scale factor from the current measurement and the target dimension, apply it, export a new file, and verify the result in the slicer.

Measure before changing the mesh

First decide which dimension must reach the target: overall length, width, height, or a specific feature. The STL Viewer reports approximate X, Y, and Z bounding dimensions, which are useful for overall size but not for every hole, wall, or distance between features. Check a known measurement in the source or destination application when precision matters.

STL does not reliably state physical units. Confirm that the current coordinate size is being interpreted as intended by the slicer or CAD application. If the model appears off by a unit conversion, correct that assumption before applying a scale; otherwise you may compound the mismatch.

Calculate the scale factor

For a uniform resize, divide the desired dimension by the current dimension measured along the same axis. Enter that result as the scale factor. A factor greater than one enlarges the coordinates; a factor between zero and one reduces them. Use the same factor on all axes when the shape's proportions must stay unchanged.

If only one dimension should change, an axis-specific factor can alter proportions. That may be appropriate for a deliberate stretch, but it changes circles, angles, wall thicknesses, and fit relationships. Do not use separate axis factors to compensate for an unknown unit problem or to force a part to fit without checking its design.

Apply scale in the STL Editor

Open the STL Editor and select the STL from your device. The editor runs locally in the browser. In the Scale controls, enter a value in Uniform to scale all axes together, or use X, Y, and Z for axis-specific changes. Select Apply scale to update the mesh preview.

Check the edited model's displayed dimensions and overall shape before exporting. The editor's controls transform the existing triangles; they do not rebuild the source CAD model, repair holes, or make a non-manifold mesh printable. Use Undo last edit if the scale was entered incorrectly, or reopen the original to start over.

Export and verify the new STL

Choose Export binary STL to save a new mesh to your device. Keep the original file unchanged so you can compare or recover it. Open the exported STL in your target slicer and confirm the exact dimensions, orientation, and placement there, because the slicer's unit interpretation is what matters for the next step.

For an assembly or fit-critical part, check the dimensions that control the fit, not just the overall bounding box. Scaling the whole mesh also changes holes, clearances, and wall thicknesses. If those features must remain exact, make the change in the original CAD design and export a fresh mesh instead of scaling the STL.

When scaling is not the right fix

Scaling does not repair open boundaries, intersecting shells, or missing geometry. If the slicer reports mesh defects, review the file with STL Repair and inspect the result separately. A warning about size should be handled as a units or transform question, not as a topology repair.

A mesh editor changes geometry without recovering editable features or design intent. If you need to revise a dimension while preserving constraints, wall thicknesses, or mating features, request the original CAD file or ask its author to export a corrected version. Verify all changes in the application that will manufacture or use the model.

Frequently asked questions