Why does changing PPI change print size?

Check the source pixels and final physical size

Resolution decisions should start with the actual pixel dimensions, the intended physical output and the target or provider-specified PPI. Metadata labels alone do not add or remove source pixels.

Apply the answer to this specific question

If pixel dimensions stay fixed, increasing PPI packs those pixels into fewer physical inches; lowering PPI spreads the same pixels across a larger print. The practical consequence should be checked with Pixels to Print Size Calculator when your own dimensions, page count, cost or production values differ from the example implied by the question.

What commonly changes the result

For “Why does changing PPI change print size?”, the most important variables are the ones represented by the linked calculator and any provider-controlled specification. A correct arithmetic result can still be unsuitable if the source dimensions, category, page yield, trim, bleed, margin or production method were assumed incorrectly.

A better verification workflow

For Why does changing PPI change print size?, record the source measurement or controlling specification first, then run the real job values through pixels to print size. Keep the result with the job notes, compare it with the physical file or material, and recheck any provider-controlled rule immediately before production or upload.

Practical answer

If pixel dimensions stay fixed, increasing PPI packs those pixels into fewer physical inches; lowering PPI spreads the same pixels across a larger print.

When the decision affects a paid print run, book upload, client order or expensive material, keep the calculation with the job notes and verify any external specification again immediately before production.

Sources