2.54 cm per inch is 12.70* 17.78 cm.

For example, 7 inches means that the photo length is 2.54x7 =17.78cm ... The 7-inch photo has a scale of 5X7 and a resolution of 1024X768.

Extended data:

The size of the photo is in inches, 1 inch =2.54cm, and usually x inches refers to the inch length of the long side of the photo. ID card, physical examination form, etc. Most of them are 22×32 mm smaller than one inch, and the second-generation ID cards are 26 mm× 32 mm. ..

Ordinary one-inch phase is 25mm×35mm. The standard photo size of passports and travel documents is 48mm×33mm, the head width is 2 1 mm ~ 24 mm, and the head length is 28 mm ~ 33 mm).

References:

Baidu encyclopedia-photo size