How is the scale factor calculated?

A part designed at dimension D cools to D times (1 minus shrinkage). To finish at the target, the model must be scaled by 1 divided by (1 minus shrinkage). For 1.8 percent ABS shrinkage that is 1 over 0.982, or about 101.83 percent.

What are typical shrinkage rates?

PLA and PETG shrink very little, around 0.3-0.4 percent. ABS is roughly 1.8 percent, ASA 1.5 percent, polycarbonate 0.7 percent, and Nylon up to 2 percent. Glass and carbon-fiber fillers reduce shrinkage compared with the unfilled base resin.

Should I apply this scale in the slicer or in CAD?

Either works for uniform parts. Slicer scaling is fast for a one-off. For parts with mixed internal and external tolerances, compensate in CAD so you can offset holes and pegs independently, since shrinkage affects external dimensions and internal cavities differently.

Why do my ABS parts come out undersized even after compensating?

Shrinkage varies with print temperature, bed temperature, part geometry, and cooling rate. The values here are starting points. Print a calibration block, measure it, and feed your measured shrinkage into the Custom field for a printer-specific result.

Does shrinkage affect holes and pegs the same way?

No. As the part shrinks, external dimensions get smaller but internal holes also get smaller (tighter). For a press fit this can help or hurt depending on which part shrinks. Compensate holes and external features separately when fit is critical.

What is the 3D Print Shrinkage & Tolerance Calculator?

Calculate the slicer or CAD scale factor needed to compensate for 3D print material shrinkage. Covers ABS, ASA, Nylon, PC and PETG with typical shrinkage rates, outputting the exact model dimension to use for a target fit. It runs free in your browser on Gera Tools, with nothing uploaded.

3D Print Shrinkage & Tolerance Calculator

Name: 3D Print Shrinkage & Tolerance Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Tight-tolerance prints in ABS, ASA, or Nylon almost always come out undersized because the material contracts as it cools. This calculator gives you the scale factor to apply so the finished, cooled part lands on your target dimension.

How it works

If a part is modelled at dimension D, after printing and cooling it measures:

printed size = D × (1 − shrinkage)

To make the cooled part equal your target, you must print it larger. Solving for the model dimension:

scale factor = 1 ÷ (1 − shrinkage)

model dimension = target × scale factor

For ABS at 1.8% shrinkage, the scale factor is 1 ÷ (1 − 0.018) = 1 ÷ 0.982 ≈ 1.0183, or 101.83%. A part that must finish at 100mm should be modelled or scaled to 101.83mm.

Typical shrinkage rates

Material	Linear shrinkage	Notes
PLA	~0.3%	Low shrinkage; suitable for dimensional parts without compensation
PETG	~0.4%	Very consistent; good first choice for functional prints
PC	~0.7%	Stiff and strong; shrinkage is consistent if printed hot
ASA	~1.5%	ABS-alternative with better UV resistance; still needs compensation
ABS	~1.8%	High shrinkage, anisotropic; X/Y may differ from Z
Nylon (PA)	~1.5–2.5%	Wide range; also absorbs moisture which changes dimensions

Glass- and carbon-filled grades shrink noticeably less than their unfilled base resin because the fibres resist thermal contraction. CF-Nylon, for instance, may shrink only half as much as unfilled PA12, which is one reason filled nylons are favoured for dimensionally critical parts.

Shrinkage is not uniform in all three axes

An important subtlety: shrinkage in FDM printing is anisotropic. The X and Y axes (within a layer) typically shrink more than the Z axis (between layers). This is because the layers cool and contract against each other in Z, while X/Y contraction is less constrained. For most functional parts the difference is small enough to ignore, but for very tight tolerances in all three dimensions, calibrate X, Y, and Z separately using a rectangular test block measured with calipers.

How holes and external dimensions respond differently

Shrinkage affects external dimensions and internal cavities in opposite directions from the perspective of fit:

External dimensions (overall length, outer diameter of a shaft) become smaller than modelled
Internal holes (bores, slots) also become smaller as the surrounding material contracts inward

For a shaft and bore press fit, both shrink, but by different amounts depending on geometry. The thicker outer walls of a bore housing shrink more absolutely than a thin-walled feature, so the bore may close up more than the shaft shrinks — and the interference becomes tighter than intended. Always measure both mating parts after printing and adjust the CAD model independently if press-fit tolerances matter.

Finding your printer-specific shrinkage

Published shrinkage rates are starting points; real shrinkage depends on:

Print temperature and bed temperature
Cooling fan speed (more cooling = faster solidification = different shrinkage)
Part geometry (thin features cool faster than thick ones)
Filament brand and lot

To calibrate: print a simple 100 × 100 × 10 mm block, let it cool fully (at least 30 minutes), measure each axis with calipers, and compute: shrinkage = (100 − measured) / 100. Enter that value in the Custom field for a result specific to your printer, filament, and profile.