How big does an engraved QR code need to be?

It depends on how much data is in it, which is why the tool shows you the module size instead of a single number.

As a rough guide, with a short link:

• About 25 mm is comfortable on most materials.
• Down to 15 mm can work on high-contrast material like acrylic or coated metal.
• A full contact card can need 50 mm or more, because it holds far more data.

The rule that actually matters: keep the module size at or above 0.6 mm to be safe, and treat 0.4–0.6 mm as testable but risky. The readout colours this in for you.

If a code is coming out too dense, shorten the content rather than shrinking the artwork.