Choose the size for the job
Match the image shape before worrying about a resolution label. A 3:2 image can fill a landscape 6 × 4 print without changing its proportions. A 4:3 image cannot do that while keeping every edge: it needs either a crop or a smaller image rectangle with borders.
| Measurement | Value |
|---|---|
| Inches | 4 × 6 |
| Centimetres | 10.16 × 15.24 |
| Millimetres | 101.6 × 152.4 |
| Short-edge-to-long-edge ratio | 2:3 |
Pixel examples
These examples multiply each edge in inches by the stated PPI. They describe pixel counts for the chosen size, not a universal pass or fail rule for appearance. Use the retained pixels after cropping when checking an existing photo.
| Example PPI | Pixels |
|---|---|
| 150 | 600 × 900 |
| 240 | 960 × 1,440 |
| 300 | 1,200 × 1,800 |
A worked example
A 3000 × 2000 file printed at 6 × 4 inches supplies 500 PPI in both directions. No crop is needed. With a 4000 × 3000 source, filling the same shape retains an ideal 4000 × 2666⅔ pixel rectangle; keeping the whole image instead places it at 5⅓ × 4 inches with one-third-inch borders on the left and right.
Before you print
A product sold as 10 × 15 cm is not mathematically identical to 4 × 6 inches: its edges are 100 × 150 mm. Read the order specification if an exact fit matters. A lab can also apply its own crop or border setting, so inspect its final preview.