Three things that trip up printing
- Not enough pixels: an image that looks sharp on screen can turn blurry when printed large.
- The wrong aspect ratio: phone photos (4:3) and common print sizes differ slightly, so edges get cut off or margins appear.
- The PDF is the wrong size: a PDF made from images is not necessarily paper-sized.
Here is how to sort all three out before printing, using this site’s tools in order.
Step 1: check how many pixels you need
In the Print Size Calculator, choose “Size to Pixels”, pick your unit (mm, cm or in) and enter the paper size. 300 DPI is the usual target for photos and flyers; around 150 DPI is common for posters viewed from a distance.
| Paper | Size (mm) | Pixels for 300 DPI | Pixels for 150 DPI | A 12 MP photo gives |
|---|---|---|---|---|
| 3.5 × 5 in print (L size) | 89 × 127 | 1051 × 1500 | 526 × 750 | 806 DPI |
| 5 × 7 in print (2L size) | 127 × 178 | 1500 × 2102 | 750 × 1051 | 575 DPI |
| A4 | 210 × 297 | 2480 × 3508 | 1240 × 1754 | 344 DPI |
| A3 | 297 × 420 | 3508 × 4961 | 1754 × 2480 | 243 DPI |
The last column shows how fine a typical 12-megapixel phone photo (3024 × 4032) prints when it fills that paper. Up to A4 it stays above 300 DPI; at A3 it drops to about 243 DPI — still a good photo print, but crop in to enlarge part of the picture and you run out of pixels fast.
Enlarging an image that has too few pixels does not add detail. When pixels are short, printing smaller is the reliable fix.
Step 2: match the aspect ratio to the paper
Most phone photos are 4:3 (1.33); a 3.5 × 5 in print is about 1.43, and A-series paper is 1 : √2 (about 1.41). Print a mismatched image “to fill the page” and the printer or print kiosk trims the edges for you. To decide what gets cut yourself, match the ratio first.
Option A: crop to fit
In Image Crop, choose a ratio such as “3.5×5 in print (landscape)” or “A4 etc. (portrait)” and the selection locks to it. Cropping a 4000 × 3000 photo to a landscape 3.5 × 5 in print removes about 6.6% of its height (197 pixels). This suits photos with something important near the edge, because you choose where the cut falls.
Option B: add margins to fit
If nothing should be cut, choose the same ratio in Letterbox Padding and add white (or any colour) margins. A 4000 × 3000 photo becomes 4281 × 3000 for a landscape 3.5 × 5 in print, with 140 pixels on each side. A 3024 × 4032 portrait photo becomes 3024 × 4277 for portrait A4, with about 122 pixels above and below.
Step 3: combine into a PDF
To print several images at once, or take them to a print shop, combine them into one PDF with Image to PDF.
That tool treats one image pixel as one PDF point (1/72 inch) and gives each image a page of the same size. A 3024 × 4032 photo therefore becomes a 42 × 56 inch page (about 107 × 142 cm). When printing, choose “Fit to page” in the print dialog.
If you matched the ratio to the paper in step 2, “Fit to page” scales the image to fill the sheet exactly, with no stray margins or cut edges.
If you are sending files to a print company
- Many ask for 3 mm of “bleed” on every side beyond the finished size. For A4, that means working to 216 × 303 mm.
- Printing converts screen colours to ink colours (CMYK), so prints can look less vivid than the screen.
- Required resolution and file formats vary by company. Always check their submission guidelines.