Choose the size for the job
The word inches matters here. A 10 × 15 cm product is much smaller than a 10 × 15 inch product. Confirm the unit in a lab order or frame listing before using the same two numbers in a calculator.
| Measurement | Value |
|---|---|
| Inches | 10 × 15 |
| Centimetres | 25.4 × 38.1 |
| Millimetres | 254 × 381 |
| 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 | 1,500 × 2,250 |
| 240 | 2,400 × 3,600 |
| 300 | 3,000 × 4,500 |
A worked example
A 6000 × 4000 landscape photograph fills a 15 × 10 inch print at 400 PPI. The same file at 12 × 8 inches gives 500 PPI, and at 18 × 12 inches gives about 333.33 PPI. All three examples retain the same composition because their aspect ratios match.
Before you print
This print is 381 mm along its long edge. A3 paper is 420 mm long and 297 mm wide, so a centred portrait print on A3 leaves 21.5 mm at each side and 19.5 mm at the top and bottom. Those are geometric spaces; check that the printer can use the required area.