Pixels and physical size need a density
Pixels describe the image grid. Millimetres, centimetres and inches describe physical size. PPI—pixels per inch—connects them: pixels = inches × PPI, and inches = pixels ÷ PPI. One inch is exactly 25.4 mm or 2.54 cm. The same pixels cover a smaller physical area at a higher PPI.
Understand the rounding
Digital images need whole pixels. Choose nearest, up or down when converting a physical size. Nearest rounds an exact half upward. The result shows your requested physical size and the actual size represented by the rounded pixel grid at the entered PPI. For example, 35 × 45 mm at 300 PPI rounds to 413 × 531 pixels using nearest; the resulting grid represents approximately 34.967333 × 44.958 mm.
Pixel rounding uses exact decimal arithmetic for the entered values. Physical results are displayed to six decimals. PPI may be 1–2,400; physical inputs are bounded to 10,000 mm per side and the final grid to 1–100,000 pixels per side. These are calculator bounds, not supported image-export sizes.
Calculate first, then resize or print
This tool produces measurements, not a resized image. It does not change metadata, add missing detail or establish document-photo acceptance. Printer DPI describes output dots and is not the same as image PPI. Printer scaling can change physical output; use actual-size printing and measure a test copy when size matters.
Optional image selection uses the shared header reader for PNG, JPG, WebP and GIF, including EXIF orientation. It keeps your entered PPI instead of assuming embedded metadata is reliable. A readable header does not verify all image content. An invalid or cancelled read leaves your entries intact; editing during a read discards the pending result.
Processing stays local with no saved draft. Downloaded reports contain the entered dimensions and calculations, not image pixels. The example is a sample calculation, not a country-specific requirement.
Inspect an image’s dimensions · Resize an image · Crop a custom ID photo