An image has no single physical print size. Its pixels can be spread over a small or large area: PPI is the number assigned to each inch.
The formula
Inches = pixels ÷ PPI. Centimetres = pixels ÷ PPI × 2.54. Calculate width and height separately. One inch is exactly 2.54 cm.
For a 3,000 × 2,000 pixel image at 300 PPI, width is 3,000 ÷ 300 = 10 in, or 25.4 cm. Height is 2,000 ÷ 300 = 6.67 in, or 16.93 cm, rounded to two decimals.
At 150 PPI, it becomes 20 × 13.33 in (50.8 × 33.87 cm). The pixel count stays the same; no new detail has been created.
Use the result
Find your file’s pixel dimensions, choose a PPI to compare and enter both sides in the print size calculator. Keep the image proportions when placing it in a document. Check the physical output: a PDF viewer or printer driver may apply another scale.
Changing a resolution label does not sharpen an out-of-focus photograph. Resampling changes the pixel count, which is a different operation. This tool relates numbers and does not process files.
For a fixed print size, select print size → pixels. The answer gives the minimum whole pixels for that target, not a quality guarantee for an image you do not yet have.
References and scope
The numerical examples are our own. Check a physical print on your own equipment.