3d Calcs
CONFIG:
130 W
$0.15/kWh
$20.00/kg spool
Utilities & 3D Tools MODULE

3D Model Scale & Unit Converter (Inch ↔ mm)

Convert between inches and millimeters (2540% scale factor), miniature scale ratios (1:12, 1:64), and auto-fit models to your build plate.

Conversion Mode
Direction
Why STL files look microscopic:

The STL file format contains only raw vertex coordinates without any unit metadata. When you design a 2-inch part in CAD and export it, the file contains the number 2.0. 3D slicers interpret every unit as millimeters, resulting in a tiny 2 mm print! Scaling by 2540% restores its true physical size.

Slicer Scale PercentageScale Factor
2540%25.4×
Inches to Millimeters Conversion

In OrcaSlicer, PrusaSlicer, or Bambu Studio, select your model, open the scale tool, and enter 2540% uniform scale.

Precision: 1 inch = exactly 25.4 millimeters
01 / PROTOCOL

Measurement & Operating Instructions

STEP 01

1. Select Mode

Choose Unit Conversion (inch ↔ mm), Miniature Scale Ratio, or Fit to Build Plate.

STEP 02

2. Pick Scales

Select standard tabletop miniature scales (Warhammer 28mm, Hot Wheels 1:64, Dollhouse 1:12).

STEP 03

3. Apply in Slicer

Enter the generated scale percentage in your 3D slicer scale tool.

02 / MATHEMATICS

3D Unit & Miniature Scale Ratio Math

Handles unit mismatches (inch ↔ mm) and standard tabletop scale conversions (1:12, 1:24, 1:64, 1:160).

Inch to mm = Scale × 2540% | Ratio Scale = (Source Scale / Target Scale) × 100%
Real-World Worked Benchmark:

To convert a model from 1:12 dollhouse scale down to 1:64 Hot Wheels scale: Scale Factor = 12 / 64 = 0.1875 (18.75% scale in slicer).

Frequently Asked Questions

Why did my STL file open microscopic in my slicer?
STL files do not store units. If a model was designed in inches (e.g. 2.0 inches wide), slicers read it as 2.0 millimeters. Scaling by 2540% (25.4 × 100) restores the intended size.
What scaling factor converts inches to millimeters for 3D prints?
Multiply by 25.4, or scale by 2540% in your slicer. To convert an STL designed in millimeters back to inches, scale by 3.937% (1 / 25.4).
What are standard miniature tabletop modeling scales?
Common scales include 28mm heroic (1:56), 32mm modern (1:50), Warhammer 40k infantry (~1:56 to 1:60), D&D grid scale (1:60, where 1 inch = 5 feet), and architectural model scales (1:50, 1:100, 1:200).
How do I scale a 3D model to fit my printer build volume?
Measure your printer's maximum X, Y, and Z limits. Divide each maximum printable dimension by the model's bounding box dimension, and take the smallest ratio. Scale uniformly by this factor.
Does scaling a 3D model change its wall thickness and bolt holes?
Yes! Uniform scaling scales all geometry proportionally, meaning a 3mm screw hole scaled to 50% will shrink to 1.5mm. For functional mechanical assemblies, resize holes in CAD rather than scaling the entire STL.
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