Every country sets its own passport photo size, and getting it even a few millimetres wrong is one of the most common reasons an application gets sent back. Here is how the main sizes compare and why they differ.
Passport photo size is set by each country's own immigration authority, not by a single global standard. Some countries, like Pakistan and most of Europe, use 35 x 45 mm. Others, including India and the United States, use a square 51 x 51 mm (2 x 2 inch) format. Gulf countries such as Oman and Saudi Arabia commonly ask for 40 x 60 mm.
A printed photo is measured in millimetres, but a digital upload is measured in pixels. The two are connected through resolution, usually 300 DPI (dots per inch) for passport photos. At 300 DPI, a 35 x 45 mm photo works out to about 413 x 531 pixels. If a photo is uploaded at a lower resolution, it can look blurry even if the millimetre size on paper is correct.
Pakistan, UK, Germany, France: 35 x 45 mm. India, USA: 51 x 51 mm. Canada: 50 x 70 mm. UAE: 43 x 55 mm. Oman, Saudi Arabia: 40 x 60 mm. China: 33 x 48 mm.
Rather than measuring by hand in an editing program, a tool that already knows each country's exact size removes the guesswork. Upass applies the correct size and background automatically once you choose your country, then exports a JPG (or PDF) at the right pixel dimensions for printing or uploading.