Generally speaking, one inch is usually 2.54cm long.
When we say inch, we mean the long side of the photo, so the length of a 9-inch photo is 9*2.54=22.86. But generally speaking, a 9-inch photo is a less common size.
:
ID cards, physical examination forms, etc. are mostly 32×22mm small, 26mm×32mm second-generation ID cards, and 25mm×35mm ordinary one-inch photos. The standard photo size of passport and travel document is 48mm×33mm, the head width is 21mm ~ 24 mm, and the head length is 28 mm ~ 33 mm).
The following are common photo sizes:
1 inch is 2.5 cm and 3.5 cm. ID photo is 3.3 cm *2.2 cm.
2 inches is 3.5 cm and 5.3 cm smaller than 2 inches (passport), 4.8 cm and 3.3 cm.
5 inches is 5 cm and 3.5 cm, 12.7*8.9,
6 inches is 6x415.2cm and10.2cm,
7 inches is 7x5 17.8 cm and 12.7 cm.
8 inches is 8x6 20.3 1 cm and 5.2 cm.
10 inch is10x8 25.42cm and 0.3cm,
12 inch is 12x 10 30.5 and cm 20.3 cm.
15 inch is 15x 10 38. 1 cm and 25.4 cm.