Almost every authority specifies its ID photo in physical units: 35 x 45 mm, or 2 x 2 inches. Upload portals cannot check physical units, because a digital image does not have a physical size until something prints it. So they restate the same rule in pixels, and the number they choose depends on the print resolution they are assuming. That is the entire source of the confusion.
The conversion, in both directions:
| Millimetres to pixels | pixels = mm ÷ 25.4 × DPI |
|---|---|
| Pixels to millimetres | mm = pixels ÷ DPI × 25.4 |
DPI — dots per inch — is the resolution you are printing at. 300 DPI is the working assumption everywhere in this field, because it is roughly where a print stops showing pixel structure at reading distance. 600 DPI is better still and costs nothing but file size.
The conversions you are most likely to need
| Physical size | At 300 DPI | At 600 DPI |
|---|---|---|
| 2 x 2 in (50.8 x 50.8 mm) — U.S., India | 600 x 600 px | 1200 x 1200 px |
| 35 x 45 mm — Schengen, UK, Australia, Japan | 413 x 531 px | 827 x 1063 px |
| 33 x 48 mm — China | 390 x 567 px | 780 x 1134 px |
| 50 x 70 mm — Canada | 591 x 827 px | 1181 x 1654 px |
| 30 x 40 mm (3 x 4 cm) | 354 x 472 px | 709 x 945 px |
| 40 x 60 mm (4 x 6 cm) — Vietnam, Indonesia | 472 x 709 px | 945 x 1417 px |
Notice the second column reading backwards: a portal asking for 600 x 600 pixels is asking for a 2 x 2 inch photo at 300 DPI, and one asking for 413 x 531 is asking for 35 x 45 mm. The pixel figure is not an alternative specification, it is the same one in different clothes. That is why choosing your document rather than a pixel count is the safer route: the physical size and head height are the rule the reviewer applies, and the pixel count follows from them. Dedicated pages exist for the common pixel requests — 600 x 600 px, 413 x 531 px, 354 x 472 px.
What actual portals ask for
| U.S. online passport renewal | Square photo, 600 x 600 px minimum. JPEG between 54 KB and 10 MB. Must be an unedited original — no replaced background. More |
|---|---|
| U.S. visa (DS-160) | Square, 600 x 600 px minimum and 1200 x 1200 px maximum, JPEG, under 240 KB, in colour. More |
| UK passport (online) | At least 600 px wide and 750 px tall — note the 4:5 ratio, matching 35 x 45 mm. File between 50 KB and 10 MB. More |
| Chinese visa (COVA) | 354–420 px wide and 472–560 px tall, JPEG between 40 KB and 120 KB — an unusually tight window in both dimensions. More |
Two patterns are worth internalising. Most portals set a minimum resolution and a maximum file size, which pull in opposite directions — more pixels means more bytes. And a few, like COVA, set a maximum resolution as well, so simply exporting at 600 DPI will fail. When a portal gives a pixel range, aim at the middle of it rather than the edge.
Why you cannot fix a small photo by raising the DPI
This is the most consequential misunderstanding about DPI, and it costs people applications. DPI is not a property stored in the pixels; it is an instruction about how large to print them. Taking a 200 x 200 pixel image and setting its DPI metadata to 300 does not create detail — it just declares that those 200 pixels should be printed across two thirds of an inch. Print it and it will look exactly as soft as it did before, because the information was never there.
What that means in practice: a passport photo has to be shot at sufficient resolution, not upscaled to it. A face cropped out of a group photo, a screenshot, or an image that has been through a messaging app cannot be rescued by resampling. AI upscalers make matters worse rather than better here — they invent plausible detail, which is both visibly synthetic to a reviewer and, for U.S. online renewal, prohibited outright as an edited photo.
The floor to aim for: your original photo should have at least as many pixels across your head as the final crop needs across the whole frame. Any modern phone camera clears that comfortably if you fill a reasonable part of the frame with your head to begin with — stand about an arm and a half from the camera rather than across the room.
Getting it right without doing arithmetic
Pick your document, and the export is produced at the right physical size and a pixel count that satisfies the portal — 600 DPI where the portal allows it, and inside the published bounds where it does not. If a form gave you only a pixel figure, use the matching size page and the millimetre equivalent is applied for you.
Frequently asked questions
What DPI should a passport photo be?
300 DPI at the required physical size is the standard assumption, and 600 DPI is better if the portal has no maximum pixel limit. Below 300 DPI a print starts to show visible pixel structure at reading distance, which reads as low quality to a reviewer.
How many pixels is a 35 x 45 mm photo?
413 x 531 pixels at 300 DPI, or 827 x 1063 pixels at 600 DPI. The formula is millimetres divided by 25.4, times the DPI.
How many pixels is a 2 x 2 inch photo?
600 x 600 pixels at 300 DPI, or 1200 x 1200 at 600 DPI. This is why U.S. portals ask for a minimum of 600 x 600 — it is the 2 x 2 inch requirement expressed at print resolution.
A portal asked for 600 x 600 pixels. What size photo is that?
A square photo, which for U.S. documents means 2 x 2 inches (51 x 51 mm) at 300 DPI. Choose the U.S. passport or visa preset rather than cropping to 600 x 600 by eye, because the head height inside that square is also specified and is what most refusals turn on.
Can I increase the DPI to meet a resolution requirement?
No. DPI metadata only states how large the existing pixels should print; it adds no detail. A low-resolution photo stays low-resolution, and AI upscaling makes it worse — the invented detail is visible to a reviewer, and for U.S. online passport renewal an AI-altered photo is refused outright. Take a new photo at a sensible distance instead.