THE METHOD
Resolution is a ratio.
Shape matters too.
Pixelready compares a source image with a physical print rectangle. It assumes centred placement, square image pixels and no enlargement or resampling of the source.
Two ways to place one image
Crop to fill covers the full rectangle. If its shape differs from the image, some source pixels fall outside the print. The effective PPI is the smaller of source width ÷ print width and source height ÷ print height, with print dimensions in inches.
Fit whole image keeps every source pixel inside the rectangle. The effective PPI is the larger of those two ratios. The printed photo may be smaller than the rectangle on one axis, leaving centred borders.
Worked example: landscape source, portrait print
Take a 6000 × 4000 pixel image and an 8 × 10 inch rectangle (20.32 × 25.4 cm). Set your own comparison target to 300 PPI.
| Quantity | Crop to fill | Fit whole image |
|---|---|---|
| Effective resolution | 400 PPI | 750 PPI |
| Source window | 3200 × 4000 px | 6000 × 4000 px |
| Printed photo | 8 × 10 in | 8 × 5⅓ in |
| Centred edge effect | 1400 px trimmed from each side | 2⅓ in border above and below |
| Source area retained | 53⅓% | 100% |
Both examples exceed the entered 300 PPI target. That is a numeric comparison, not a quality rating or a recommendation to use one placement.
Worked example: the same shape
A 2400 × 3000 pixel image in an 8 × 10 inch rectangle has the same 4:5 shape. Both modes give 300 PPI, use the full image, and leave no border or trim. At an entered target of 301 PPI, the result is below that target.
Native size at your target
Divide the full image’s pixel dimensions by your target PPI. A 6000 × 4000 image at an entered 300 PPI gives 20 × 13⅓ inches (50.8 × 33.867 cm, rounded). This retains the source image’s shape. It does not imply that it fits the chosen print rectangle without a border or crop.
Units, rounding and comparisons
One inch is 2.54 cm or 25.4 mm. Unit changes preserve each entered physical distance internally rather than repeatedly rounding and converting the displayed number. Editing a displayed value deliberately sets a new distance.
The target comparison uses exact decimal ratios from the entered values, so a unit round trip does not turn a true boundary result into a pass or fail. The visible outputs are rounded for readability. Ideal crop windows and centred edges can be fractional pixels; actual image-editing software may round its crop edges.
What the calculation cannot assess
No image is uploaded or inspected. The calculator cannot determine sharpness, lens focus, compression damage, colour rendering, paper finish, the printer’s settings or a suitable viewing distance. It does not edit image metadata or create extra image detail. Consult your print provider’s requirements when choosing your own PPI target.