Passport photo size in pixels

Pixels are meaningless without a DPI

This is the core idea and it is worth being precise about. A specification says the photo must be 35 mm wide. A pixel count says how much data describes that width. The bridge between them is DPI, dots per inch. At 300 DPI, 35 mm needs 413 pixels; at 600 DPI it needs 827. Both files print as an identical 35 mm photo, one just carries four times the data.

So when a tool tells you a passport photo is "413 by 531 pixels" without mentioning DPI, it has quietly assumed 300 for you. That is usually the right assumption, but it is an assumption.

Why official pixel minimums look arbitrary

IRCC asks for at least 420 by 540 pixels. The Singapore ICA asks for at least 400 by 514. Chinese visa uploads want 354 by 472 up to 420 by 560. These are not arbitrary: they are rounded results of converting a millimetre size at some assumed DPI. IRCC's 420 by 540 is a clean 7:9 ratio, exactly the shape of a 35 by 45 mm photo.

Recognising the ratio is useful, because it tells you the authority cares about shape and minimum detail rather than a specific pixel grid. Anything larger with the same ratio is normally fine.

The DPI metadata problem

There is a failure mode here that catches almost every browser-based photo tool. When a canvas is exported to JPEG, the encoder writes a JFIF density of 1 by 1 with the units field set to "no units", meaning the file declares no physical size. Printers and photo labs then fall back to their own default scaling, and a pixel-perfect crop comes out at the wrong physical size on paper.

The fix is to patch the JFIF density fields after encoding so the file carries a genuine DPI. This site does that on every export. If you use another tool, print one copy and measure it with a ruler before committing to a full sheet.

Choosing dimensions when a KB limit applies

More pixels means a larger file, so pixel and file size limits fight each other. The US is the tightest case at 600x600 minimum and 240 KB maximum. In that situation, staying near the lower end of the pixel range leaves more room for quality. Where the ceiling is generous, as with IRCC's 4 MB, go well above the pixel minimum instead.