Photo print sizes in pixels, and what labs really need

What are the standard photo print sizes in pixels?

Multiply each side in inches by the DPI. At 300 DPI, the usual figure for a photo print, a 4 inch side is 1200 pixels. The 125 DPI column is the minimum Nations Photo Lab states for its prints.

The shape is each print's width to its height in lowest terms. A photo of a different shape is cropped to fit, so the shape matters as much as the pixels.

To set the DPI a file declares without touching its pixels, use the tool to change image DPI. It lists the most common prints at 150 DPI too.

For why the DPI changes the print and nothing else, read what DPI means, and what it does not change.

Do you really need 300 DPI?

No. 300 is the figure labs give for their best quality. The same labs print from far fewer pixels, and say so.

Shutterfly publishes a chart of the smallest photo it recommends for each print. We worked out how many pixels per inch each one leaves once the photo is scaled to cover the paper.

The figures are from Shutterfly's upload guide, which also puts a 2400 x 3600 photo on a 24 x 36 poster. Nations Photo Lab's pixel chart calls 125 PPI its minimum and 300 its best quality.

So a 12 MP phone photo, 4032 x 3024, is plenty for any print up to 8 x 10 at 300 DPI. A photo below the 125 column will print, but soft.

Which print is the shape of a phone photo?

A 12 MP phone photo is 4 by 3. Of the prints in the chart, only 4 x 5.3 and 6 x 8 share that shape, so they are the only ones that print it whole.

Walgreens sells 4 x 5.3 as True Digital Prints, which it says better match the photos most digital cameras produce. Walmart lists 4 x 5.3 among its standard prints as well. The exact size is 4 x 5.33 inches.

Every other print crops a phone photo. A 4 x 6 loses about 11 percent of its width. The page to resize an image in inches shows how much each print keeps.

Is 10 x 15 cm the same as 4 x 6 inches?

Almost. 10 x 15 cm is 3.94 x 5.91 inches, a little smaller, but the same 2 by 3 shape. Wikipedia's table of photo print sizes pairs each metric print with the inch one it stands in for.

The last column is how much of a file made for the inch print survives on the metric one. Where the shapes match, nothing is cropped. Where they differ, about 1 percent is.

So you can send a 1200 x 1800 file to a lab printing 10 x 15 cm, and it prints whole. To work in centimetres instead, resize an image in cm or mm.

How do you make a photo print at the right size?

Resize it to the print's pixels and save the DPI in the file. These pages open at the size with 300 DPI already set: resize an image to 4 x 6 inches, 5 x 7 inches and 8 x 10 inches.

For 4 x 5.3, open the inch tool and type 1200 x 1600 pixels, the exact 3 by 4 shape. Typing 5.3 inches gives 1590, which crops a sliver.

When you print at home, choose actual size, or 100 percent, rather than fit to page. A lab prints to the paper size you order, so there the shape is what counts.