Do 3D Printed Parts Shrink?

Yes. Plastic goes into the nozzle at around 200-260°C and ends up at room temperature. It contracts on the way. Every thermoplastic does this, and no printer setting abolishes it — the good ones just compensate for it.

Shrinkage matters because it is the reason a part drawn at exactly the right size comes out slightly the wrong size.

Roughly how much, by material

Treat these as the order of magnitude, not a specification. Real numbers move with geometry, temperature, part size and even the specific spool.

• PLA — around 0.2-0.5%. The least troublesome material there is, which is why it is the default for dimensionally fussy prototypes.
• PETG — around 0.4-0.8%. Noticeable on a large part, rarely a problem on a small one.
• ABS / ASA — around 0.6-1.5%. This is the big one. On a 200 mm part that is a couple of millimetres, which is why big ABS parts warp and lift, and why they need an enclosure. See can ABS be 3D printed and ASA vs ABS.
• Nylon — around 1-2%, and it then absorbs moisture from the air and grows again. See nylon and carbon fibre parts.
• Carbon-fibre-filled grades — the fibres restrain the plastic, so filled nylon or filled PETG shrinks and warps appreciably less than the unfilled version. That is one of the main reasons to use them.
• TPU — shrinks modestly, but it is flexible, so a fit is forgiving anyway.

Slicers apply a scaling factor to compensate. It works, up to a point — the point being that shrinkage is not uniform.

Why it is not uniform, and why that is the real problem

If everything shrank by the same percentage in every direction, you would scale the model and be done. It does not.

• Z shrinks differently from X and Y. Layers are compressed on top of each other, so vertical behaviour is not the same as in-plane.
• The bed holds the bottom still. The first layers are stuck down and cannot contract; the upper layers can. That differential is exactly what warping is — the part curls up at the corners trying to relieve it.
• Thick sections shrink more than thin ones, because there is more hot plastic cooling.
• Holes go small; posts go big. As a ring of plastic cools it pulls inward on itself, so the hole closes up. The outside of a boss pulls inward too — but the bead also bulges outward slightly under pressure. A 5 mm hole commonly measures around 4.8 mm. This catches everyone, every time.

That last one is worth memorising: holes shrink, posts grow, and both errors work against you when you try to fit one into the other.

What to do about it

• Do not draw a fit at nominal. Add clearance deliberately. Our tolerances and fit guide has starting numbers for press, sliding and free fits.
• Tell us which dimensions are critical. This is the single most useful thing you can say. Error has to go somewhere; let us put it where it does no harm.
• Print a test coupon. Just the hole, boss or pocket — minutes and a few grams. Then print the real part once, correct. Reprints are the expensive option.
• Choose the material for the tolerance. If a big part must be dimensionally tight, PLA or PETG will behave far better than ABS. That is a real reason to pick a material.
• Drill critical holes. A printed pilot and a drill bit gets machining accuracy in seconds.
• Design in adjustment. A slot and a screw beats a fit that has to be perfect.

Where this is the wrong process

If your part needs to hold a dimension to better than about ±0.1 mm, or hold it across a wide temperature range, FDM is not the tool — printed plastic keeps moving with heat and, for nylon, with humidity. That is a machining job, in plastic or metal. The same goes for any inspection gauge or reference fixture: it needs to be stable, and a printed part is not. We will say so rather than sell you a part that measures wrong.

For everything else, which is most parts, this is just arithmetic you do at the design stage.

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