0.2 to 0.5% of nominal, which is the lowest contraction of any common filament.
Across a 100 mm dimension that means a finished part measuring between 99.8 and 99.5 mm. Across a 20 mm feature it is a tenth of a millimetre at worst, which most people never notice and never need to correct.
Where it stops being negligible
Long dimensions and tight fits, and the two together.
- A 40 mm dimension at the top of the range loses 0.20 mm — already enough to spoil a press fit
- A 200 mm dimension loses between 0.4 and 1.01 mm, which will visibly fail to line up with a drilled hole pattern
The threshold is usually somewhere around 100 mm for parts that must mate with something else, and much shorter for anything with an interference fit.
It is not the same in every direction
PLA's contraction is not isotropic. X and Y contract fairly freely as the part cools; Z is restrained by the layers already bonded to the plate below, so it shrinks less.
Compensating with a single uniform scale factor therefore over-corrects the vertical dimension. If a part has to be accurate in all three axes, compensate X and Y and leave Z alone — which is why the shrinkage tool on this site asks which axis you are correcting.
The blends behave the same
PLA+, silk, matte and high-speed PLA all carry the same 0.2 to 0.5% band. The toughening and pigment additives change strength, finish and density without meaningfully changing contraction.
Wood-filled PLA is the mild exception at 0.2 to 0.6%, because the wood particles behave differently from the polymer around them.
What to do about it
For most PLA printing: nothing. It is genuinely below the noise floor of a well-calibrated machine.
When it matters, measure rather than assume. Print a test dimension, measure it with calipers, and let the compensation tool derive the scale factor from what your machine and your spool actually did — that number folds in flow calibration error as well as material contraction.
Compute a correction for your own dimension in the shrinkage calculator, and see the general method in the shrinkage and tolerance guide.