Spec sheets look intimidating because they mix three different unit systems on one line: millimetres for paper, pixels for uploads, dpi for print resolution. Once you know which number belongs to which layer, every country’s sheet reads the same way.

The three layers

Print size (mm or inches). The physical photo: 2×2 in for the US, 35×45 mm for the ICAO family, 50×70 mm for Canada, 33×48 mm for China’s paper spec. This is what the officer measures at the counter.

Digital pixels (px). What the portal checks at upload. Sometimes a window (US: 600–1200 px), sometimes a minimum (UK: ≥600×750 px), sometimes an exact number (India passport: exactly 630×810 px; DV lottery: exactly 600×600 px). “Exactly” means exactly — 629 px fails.

Resolution (dpi). Only meaningful when pixels meet paper: px = mm ÷ 25.4 × dpi. Labs print at 300 dpi, which is why 35×45 mm ↔ 413×531 px keeps appearing. For uploads, dpi is metadata the portal ignores.

Head size: one measurement, many bands

“Head size” is always the crown-to-chin distance — top of the head including hair to the bottom of the chin — expressed either in mm on the print or as a percentage of the frame height. The bands diverge:

Spec	Head band	As % of frame
US passport/visa	25–35 mm of 51 mm	50–69%
UK passport	29–34 mm of 45 mm	64–76%
Schengen / ICAO family	32–36 mm of 45 mm	71–80%
India passport (2025)	face 80–85% of height	80–85%
Canada passport	31–36 mm of 70 mm	44–51%

Same face, five different correct framings — this is why a photo cropped for one country fails another even when the paper sizes match.

File limits: read both ends

Upload specs quote a byte window, and both ends bite. The US caps at 240 KB; the UK floors at 50 KB; India enforces ≈10–250 KB from both directions. A heavily compressed “optimized” JPEG can fail the floor; a raw phone export fails the ceiling. Target the middle of the window.

The soft rules

“Plain light background” means one untextured light tone — white, off-white, grey or cream per the country — with no shadow behind the head. “Neutral expression” means mouth closed, eyes open, no smile. “Recent photo” is usually six months (UK online: one). Glasses read literally: not allowed (US, India, China; Australia since 2018 — medical exemption only), allowed without glare (UK, Canada), or discouraged (Schengen).

When two documents disagree — portal vs printed checklist — the spec change log shows how often portals are the stricter document. For the standard most of these derive from, see ICAO 9303 explained.

Frequently asked questions

How many pixels is a 35×45 mm photo?

It depends on resolution: pixels = mm ÷ 25.4 × dpi. At the lab-standard 300 dpi, 35×45 mm is 413×531 px; at 600 dpi it's 827×1063 px. When a spec fixes the pixels exactly — like India's 630×810 — that's a digital requirement, not a print resolution.

Does dpi matter for an online upload?

Almost never. Portals check pixel dimensions and file bytes, not the dpi field in the metadata — a 72 dpi and a 600 dpi file with identical pixels are the same upload. dpi only becomes real when the photo is printed.

Is 'head size' measured the same way everywhere?

The measurement is the same — crown (top of head, hair included) to bottom of chin — but the allowed band differs: 25–35 mm for the US, 32–36 mm for Schengen, a percentage band (80–85%) for India. Always check which band the specific document uses.

What does 'plain light background' actually allow?

A single untextured light tone — white, off-white, light grey or cream depending on the country — with no visible shadow behind the head. What's banned everywhere is patterns, scenery, other people and strong gradients.