How to Resize an Image for Printing
Print sizes are in inches, but image files are in pixels. Here is the conversion for common print sizes, why the shape matters more than the size, and how to set the inches when you print.
To resize an image for printing, multiply the print size in inches by 300 to get the pixels you need, then resize the image to that many pixels. A 4 x 6 inch print needs 1200 x 1800 pixels. An image file has no inches of its own, so the inches are something you set again when you print.
That is why Resize Image asks for pixels only. It has a width field, an optional height field and an aspect-ratio lock, and no box for inches or DPI. The arithmetic below fills that gap. Everything runs in your browser and the photo is never uploaded.
How many pixels does each print size need?
At 300 pixels per inch, the usual target for photo prints you hold in your hand, these are the pixel sizes:
| Print size | Pixels at 300 PPI | Shape |
|---|---|---|
| 4 x 6 in | 1200 x 1800 | 2:3 |
| 5 x 7 in | 1500 x 2100 | 5:7 |
| 8 x 10 in | 2400 x 3000 | 4:5 |
| 8.5 x 11 in (US Letter) | 2550 x 3300 | a little wider than 3:4 |
| A4 (210 x 297 mm) | 2480 x 3508 | about 1:1.41 |
For any other size, it is inches x 300 on each side. For millimetres, divide by 25.4 first. Why 300, and why the number is a label rather than a setting, is covered in what DPI means and PPI vs DPI.
Do you have enough pixels?
Run the sum backwards before you resize: pixels divided by 300 is the largest sharp print. A 4032 x 3024 phone photo works out to 13.44 x 10.08 inches, so an 8 x 10 is comfortable. A 1080 x 1080 image saved from social media comes to 3.6 inches square, too small for a 5 x 7.
If you come up short, resizing up will not fix it. Resize Image will accept a width larger than your photo, but it only stretches the pixels that are there, and the print comes out soft. Find the original file, or print smaller. Resizing without losing quality explains why enlarging can't add detail.
Why the shape matters more than the size
Most phone photos are 4:3. A 4 x 6 print is 2:3, an 8 x 10 is 4:5. With the aspect lock on, Resize Image keeps your photo's shape: type a width of 1200 into a 3024 x 4032 photo and you get 1200 x 1600, not 1200 x 1800. With the lock on, the two fields stay tied to your photo's shape: change the height to 1800 and the width jumps to 1350, so you still don't get 1200 x 1800. Untick the lock and type both numbers and you get exactly 1200 x 1800, with everyone in the picture stretched.
The fix is to crop to the print's aspect ratio first, then resize.
How to resize an image for printing, step by step
- Work out the pixels. Use the table, or inches x 300 per side.
- Crop to the print's shape. Open Crop Image. Its Photo (3:2) preset is a landscape box, right for a 6 x 4 landscape print. For a portrait 4 x 6, or for 5 x 7 and 8 x 10, leave it on Free and type the width and height of the crop in pixels: 2688 x 4032 is the 2:3 crop of a 3024 x 4032 photo. Drag the box to choose what stays in.
- Resize. Drop the cropped file into Resize Image, keep the lock ticked and type the width, say 1200. The New size readout shows the result before you click.
- Download and check the file type. Resize Image saves the result as a PNG but keeps your original file name, so a resized photo.jpg is PNG data named .jpg. If your print service only takes JPG, rename the file to .png and run it through PNG to JPG.
- Set the inches when you print. Pick the 4 x 6 (or whichever) size in the print dialog, or place the image in a document at the exact size and print at 100% scale.
Why the file doesn't remember the inches
The only place a file can store a print size is a density (DPI) tag, and the PNG that Resize Image produces doesn't have one. We checked the output: it carries no density chunk at all, so the printing app falls back on its own default. That is why step 5 matters. Printing passport photos at home walks through the document method for when a size has to be exact to the millimetre.
FAQ
Can I type inches into babapic's resize tool?
No. Resize Image takes pixels only. Multiply inches by 300 and type that.
What size should I resize a photo to for a 4x6 print?
1200 x 1800 pixels, after cropping it to 2:3.
More resize walkthroughs are in the guides.