Image file size, dimensions, and PPI explained
File size measures bytes; dimensions measure pixels. Print dimensions also depend on PPI. To meet an exact square requirement without stretching, crop to fill or place the full image on a padded square canvas.
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Bytes and pixels answer different questions
A 300 × 300 image contains 90,000 pixels, but there is no single KB value for it. Content, transparency, format, and encoder settings determine its file size. A simple graphic and a detailed photograph can have the same dimensions and very different byte counts.
Compression changes how image information is stored. Resizing changes the pixel dimensions. Format conversion changes the encoded format. These operations may be combined, but they solve different requirements.
Choose a fit mode deliberately
| Mode | Output behavior | Use when |
|---|---|---|
| Fit within dimensions | Preserves ratio inside maximum bounds; may be smaller than the entered box. | You have maximum width or height. |
| Crop to fill | Fills the exact canvas and cuts off overflow. | Every output pixel must be filled and edges can be removed. |
| Fit with padding | Keeps the full image inside an exact canvas. | You need exact dimensions without cutting off content. |
Convert millimeters or inches to pixels
Use pixels = inches × PPI. For millimeters, divide by 25.4 first; for centimeters, divide by 2.54. Whole-pixel dimensions require rounding.
For example, 35 × 45 mm at 300 PPI produces approximately 413 × 531 pixels. This is a unit-conversion example, not a claim that the photo meets a country’s identity-document rules.
FileFit uses the selected PPI to calculate pixels. Do not assume it embeds a print-resolution metadata tag. Set the intended physical print size or matching PPI in your print software, with automatic scaling disabled.
Make a 300 × 300 pixel image
- Open Resize Image and set Units to px.
- Enter 300 for width and 300 for height.
- Choose Crop to fill if the edges can be cut, or Fit with padding to retain the full image.
- Resize and confirm 300 × 300 in the result. Check the KB limit separately if the destination specifies one.
Try the relevant tools
Sources and implementation
Tool behavior is documented in How FileFit works. Examples are instructional, not a promise about every file. Report a correction.