Dimensional Compensation Calculator

Most 3D printers print parts that are slightly too large or too small compared to the model. The deviation comes from material shrinkage during cooling, over-extrusion, or thermal expansion of the build plate. For functional parts — gears, press-fit inserts, hinges, snap fits — even 0.1-0.2 mm of error matters.

Horizontal expansion is a per-side offset applied in the slicer (available in PrusaSlicer, OrcaSlicer, Cura). If a part measures 50.4 mm but should be 50.0 mm, the part is 0.4 mm too large overall — 0.2 mm per side. Setting horizontal expansion to -0.2 mm tells the slicer to shrink every external wall inward by 0.2 mm.

Horizontal expansion = (target - measured) / 2

A negative result means the part is printing too large (apply the value — it will be negative in the slicer too). A positive result means the part is too small (apply a positive offset or increase extrusion multiplier instead, as small deviations are often an extrusion issue rather than a geometry issue).

Scale factor corrects the entire model proportionally. It is most useful when the error scales with the dimension — a sign of a steps-per-mm or belt pitch problem rather than extrusion width:

scale_factor = target / measured x 100 (%)

Which to use. Horizontal expansion corrects consistent fixed-width errors (the extrusion is physically slightly wider than expected). Scale factor corrects proportional errors (every feature is X% too large or too small). For most FDM printers with properly calibrated E-steps, horizontal expansion is the right tool. Scale correction is more relevant after major hardware changes.

Measure multiple features. Take at least three measurements on different areas of the print and average them. A single outlier can mislead you.