Shrinkage varies enough between materials that guessing is risky
PLA and PETG shrink comparatively little and predictably as they cool; ABS/ASA and Nylon shrink more, and less predictably, since their shrinkage depends heavily on cooling conditions like chamber temperature and part geometry. A single blanket shrinkage percentage applied across every material would be meaningfully wrong for at least some of them. This tool only applies a correction when you supply a real measured percentage, and explains exactly why the coupon test matters more for the higher-shrinkage materials.
How the allowance works
Without a measured shrinkage percentage, the tool shows no predictive guarantee and proposes printing a simple dimensioned test coupon (a bar or a flat plate) to measure your printer's actual shrinkage in that material. Once you have a measured percentage, the tool scales your nominal target dimension up to compensate, so the printed part lands closer to your intended size.
Worked example
A 100 mm target dimension in ABS/ASA, no measured shrinkage supplied: since ABS/ASA has a general high-shrinkage tendency and shrinks less predictably than PLA or PETG, the tool recommends printing a dimensioned coupon before scaling anything, rather than assuming a typical percentage that could be meaningfully wrong for your enclosure and cooling setup.
A common mistake
A frequent error is measuring shrinkage on a small coupon and applying the same percentage to a part many times larger without re-checking. Shrinkage does not always scale perfectly linearly with size, especially for a high-shrinkage material like ABS/ASA, so a percentage that was accurate on a 20 mm test cube is not guaranteed to hold on a 200 mm part.
Limitations
This deliberately does not guess a default shrinkage correction. Especially for a high-shrinkage material like ABS/ASA or Nylon, an unmeasured assumption can be wrong enough to matter; a real coupon measurement on your own printer is the reliable path.