How do I calculate a 3D print scale percentage?

Divide the target size by the original size and multiply by 100: scale% = (target / original) × 100. For example, scaling a 40 mm part to 55 mm needs 55/40 × 100 = 137.5%. Enter that percentage in your slicer's uniform scale field.

Will scaling one axis change the others?

In uniform (proportional) scaling, yes — every axis is multiplied by the same percentage so the model keeps its shape. If you only want one axis to change while the others stay fixed, use per-axis mode and turn off 'uniform scaling' in your slicer.

What does per-axis scaling do?

Per-axis scaling applies a different percentage to X, Y and Z. This stretches or squashes the model. The calculator computes each axis percentage independently and warns you when they differ, because unequal scaling distorts the geometry and can ruin fits and round features.

Does scaling affect wall thickness?

Yes. Scaling down also shrinks walls and small features, which may fall below your nozzle diameter and fail to print. After scaling, check that the thinnest walls are still at least one or two line widths thick, and that holes and pins are large enough to survive the slicer.

Why is my scaled part the wrong size after printing?

If the slicer percentage is correct but the print is off, the cause is usually printer calibration — steps-per-mm, flow, or thermal shrinkage — not the scale math. Calibrate your axes and material shrinkage first, then apply the scale percentage from this calculator on top of a well-calibrated machine.

What is the 3D Print Scale Factor Calculator?

Computes the uniform or per-axis scale percentage to type into your slicer to resize a 3D model from its original size to a target size. Handles proportional scaling from one known axis and independent X/Y/Z scaling with a distortion warning. It runs free in your browser on Gera Tools, with nothing uploaded.

3D Print Scale Factor Calculator

Name: 3D Print Scale Factor Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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When a downloaded or designed model is the wrong size, you don’t re-model it — you scale it in the slicer. The slicer expects a percentage, where 100% is the original size. This calculator works out the exact percentage to type in, either to resize the whole model proportionally from one known dimension, or to scale each axis independently when you need to stretch or squash a part.

How it works

Scaling is a simple ratio of target size to original size, expressed as a percentage:

scale% = (target / original) × 100

In uniform mode you give one original dimension and the target you want; that same percentage applies to all three axes so the model keeps its proportions. In per-axis mode each axis gets its own percentage:

X% = targetX / originalX × 100, and likewise for Y and Z

If the three per-axis percentages come out equal, the scale is uniform and nothing is distorted. If they differ, the model is stretched — you must disable “uniform scaling” in the slicer for the per-axis values to take effect.

Example

A model is 40 mm wide and you need it 55 mm wide:

scale% = 55 / 40 × 100 = 137.5%

Enter 137.5% as the uniform scale; the height and depth grow by the same factor, so a 30 mm tall model becomes 41.25 mm tall.

When to use per-axis scaling

Per-axis scaling is less common but has real applications. If you are printing a gasket that must fit an existing cutout exactly, you may need to stretch it in X but not Y. If you are compensating for systematic shrinkage that affects only one axis of your printer — a known calibration issue on some CoreXY machines — you can correct just that axis without disturbing the others. The calculator flags when the three percentages differ, which is the cue to turn off uniform scaling in your slicer and enter each value manually.

Common mistakes

Scaling a model that was designed for a different nozzle size. If the original was designed for a 0.4 mm nozzle and you scale it to 50%, the walls become 0.2 mm thick — below the nozzle diameter and impossible to print. Check wall count after scaling.
Scaling without knowing the original dimension. Many STL files have no embedded units. Open them in your slicer first to see the current bounding box before entering an original size.
Expecting a scaled model to clear shrinkage. Scale percentages and material shrinkage are separate corrections. Apply scale first, then add any shrinkage compensation on top.

How to find the original dimension

If you are not sure what dimension the STL was authored at, import it into Cura, PrusaSlicer, or Bambu Studio and hover over the model — the bounding box shows X, Y, Z in millimetres. That is your original size input.

Notes

Scaling changes everything, including wall thickness and small features. When you scale down, confirm the thinnest walls are still at least one to two nozzle widths thick or they will not print; when you scale up, watch that the part still fits the build plate. If a correctly-scaled print still measures wrong, the problem is printer calibration (steps-per-mm, flow, shrinkage), not the percentage. All calculations run locally in your browser.