The basic math in one paragraph
Photo-book providers print at roughly 250–300 dpi (dots per inch). From that follows the only formula you need: centimeters ÷ 2.54 × 250 = required pixels. An image printed 20 cm wide thus needs about 2000 pixels of width. Anything above is reserve; well below becomes visibly soft. The full derivation, including viewing distance, is in DPI and PPI explained — for the photo book the tables here are enough.
Pixel table for common book formats
Required image dimensions at 250 dpi, each for the full page:
| Book format | Full page | Double page (panorama) |
|---|---|---|
| Small / square (≈ 14 × 13 cm) | ≈ 1400 × 1300 px | ≈ 2800 × 1300 px |
| Standard A4 portrait (21 × 28 cm) | ≈ 2100 × 2800 px | ≈ 4200 × 2800 px |
| Large landscape (28 × 21 cm) | ≈ 2800 × 2100 px | ≈ 5500 × 2100 px |
| XL landscape (≈ 38 × 29 cm) | ≈ 3700 × 2900 px | ≈ 7400 × 2900 px |
For context: a current smartphone photo has 4000 × 3000 px or more — so originals are plenty for almost everything up to the A4 page. It gets tight in exactly two places: on double pages and with images that are no longer originals.
Trap 1: the double page
The panorama across both pages is every photo book's showpiece — and the most common place for the warning triangle, because it demands double the width. Add the crop: a 4:3 photo has to be cropped heavily top and bottom for a 2:1 double page, which costs extra pixels. Before planning it in, check the actual dimensions — via right-click → Properties or with the image-info tool. And when shooting on your next holiday: the phone's panorama mode delivers double-page material for free.
Trap 2: images that are no longer originals
The warning triangle almost never hits your own camera photos — but the second-hand images:
- WhatsApp versions: scaled down to messenger size — barely enough for a small image in the layout, not for half a page. For group photos from the party, ask the senders to send the originals as a document (here's how).
- Shared iCloud albums: deliver at most 2048 px — meant for screens, not for print. Ask the owner for the originals; more on sharing photos from events in a dedicated post.
- Social media downloads:Instagram & co. scale down to about 1080 px — a stopgap for stamp size, nothing more.
- Screenshots of photos: only have screen resolution and often interface remnants at the edge. Always get the photo itself.
What NOT to do before the photo-book editor
As much as we recommend compression tools here — for the photo book, images are not shrunk or compressed beforehand. Web optimization and print preparation are opposites: for the web every kilobyte counts, for print every pixel. The untouched originals belong in the photo-book editor; the provider software handles shrinking for upload itself, matched to the ordered print size. The only sensible pre-work on the image itself: straighten the horizon and roughly crop — both cost hardly any pixels and save time in the editor.
The 10-minute preparation
- Copy your selection into a folder — originals, not messenger versions (rule of thumb: files under 1 MB are suspect).
- Name candidates for the cover and double pages and check their pixel dimensions against the table above.
- Replace or plan smaller for images that are too tight — a sharp half-page image beats any mushy double page.
- Sort portrait/landscape: a landscape book and all portrait photos means many crop compromises — let the format majority of the images co-decide the book format.
If after the photo book you want to print individual images as posters: the math for that — including when viewing distance forgives lower dpi — is in Is my iPhone photo good enough to print?
Sources
CEWE — Help and print quality · Apple — Shared albums: resolutions.