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. The United States uses a square 51 x 51 mm (2 x 2 inch) format, and Canada uses 50 x 70 mm. India uses 35 x 45 mm for its passport. Oman asks for 40 x 60 mm, and some other Gulf countries use similar larger formats.
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, India, UK, Germany, France, Italy, Australia, Japan: 35 x 45 mm. USA: 51 x 51 mm. Canada: 50 x 70 mm. Oman: 40 x 60 mm. Hong Kong: 40 x 50 mm. Malaysia: 35 x 50 mm. Turkey: 50 x 60 mm. China: 33 x 48 mm. Spain: 26 x 32 mm. Always confirm with your own passport office before printing.
Rather than measuring by hand in an editing program, a tool that already knows each country's exact size removes the guesswork. Uphoto 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.