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“Scan at 300 DPI” — from a phone that has no DPI setting
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The short answer. DPI = pixels ÷ inches. A US Letter page is 8.5×11 inches, so 300 DPI means about 2550 × 3300 pixels of page. Any modern phone exceeds that easily — as long as the page fills the frame.
Almost every agency asks for 300 DPI. No phone camera offers that setting, which makes the instruction look impossible. It is not: DPI is not a camera setting at all, it is the result of a division, and once you see the arithmetic you can tell instantly whether a photo qualifies.
What DPI really is
Dots per inch is a ratio between a number of pixels and a physical size. A file does not have a DPI until you say how big it is meant to be on paper. The same 2550×3300 image is 300 DPI on a Letter page and 150 DPI on a poster twice the size. That is why your camera has no DPI setting: it does not know what size you intend to print.
The arithmetic, for the usual page sizes
| Page | Inches | Pixels needed for 300 DPI |
|---|---|---|
| US Letter | 8.5 × 11 | 2550 × 3300 |
| A4 | 8.27 × 11.69 | 2480 × 3508 |
| US Legal | 8.5 × 14 | 2550 × 4200 |
| ID card (CR80) | 3.37 × 2.13 | 1011 × 638 |
Why your 12-megapixel photo can still fail
A 12 MP phone photo is around 4032×3024 pixels — comfortably more than 300 DPI needs. It fails when most of those pixels are not the document. Photograph a page from far away, with desk and hands around it, and the page itself might occupy only 1400 pixels across. Cropping afterwards cannot invent detail: those are the only pixels that ever existed.
So the rule that matters is not megapixels. It is: fill the frame with the page.
How to actually get there
- Put the document on a flat surface with even light — near a window, not under a ceiling lamp that casts your own shadow.
- Hold the phone parallel to the page, directly above the centre. Shooting at an angle loses resolution on the far edge and distorts the shape.
- Move close enough that the page nearly touches all four edges of the frame. A small margin is fine; a desk in shot is not.
- Tap the screen to focus on the text, and hold still. Blur destroys effective resolution no matter how many pixels the sensor recorded.
- Do not use flash. It creates a bright blown-out patch that usually lands on exactly the field a reviewer needs.
Is more than 300 DPI better?
No, and it costs you. 600 DPI quadruples the file size for detail a reviewer will never look at, and it is the fastest way to run into an upload size limit. 300 DPI is the standard because it is where printed text stops improving to the human eye. Go above it only for an archival copy you intend to keep.
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Open DocSupraHow to check the DPI of a document, properly
Every image file can carry a DPI number in its metadata, and that number is a note, not a measurement. Software writes it, software ignores it, and it survives operations that halve the actual detail. The real resolution is arithmetic, and you can do it in your head.
The short answer. Divide the pixel width by the page width in inches. A file that is 2550 pixels wide across an 8.5 inch page is 300 DPI, whatever the metadata says. A file 1000 pixels wide across the same page is 118 DPI, even if it is tagged 300.
The calculation
DPI = pixels ÷ inches. For a US Letter page, 8.5 × 11 inches:
| Pixel width | Real DPI across a Letter page | Verdict |
|---|---|---|
| 2550 px | 300 DPI | Scan grade |
| 2125 px | 250 DPI | Readable, below most specs |
| 1700 px | 200 DPI | Fine for email, short of filing specs |
| 1000 px | 118 DPI | Small print starts breaking up |
For A4, use 8.27 × 11.69 inches. For a card-sized document, measure the card, not the page.
Why the tag lies
The DPI field is metadata: a note attached to the file saying what physical size it was intended to print at. Nothing enforces it. Resize an image to a quarter of its pixels and the tag can survive untouched, so the file still claims 300 DPI while carrying the detail of 75. Screenshots, exports from chat apps and anything that has passed through a messaging service are the usual offenders.
This matters because a reviewer does not check the tag. They open the file and look at it.
Where to find the pixel dimensions
- Windows: right-click the file → Properties → Details → Dimensions.
- macOS: select the file → Get Info → More Info → Dimensions.
- iPhone / Android: open the photo, swipe up or tap the information icon.
- Inside a PDF: harder, because the page and the image can differ. Open it at 100% and compare against the page size, or use software that reports the embedded image size.
The one that catches everyone
Sending a document through a messaging app and then downloading it back. Most of them re-compress and resize on the way through, sometimes to a fraction of the original. The file opens, looks fine on a phone screen, and carries a third of the detail it started with. If a document has been through a chat, go back to the original.
What to do when the DPI is too low
Nothing in software can add detail that was never recorded — enlarging the pixels makes them bigger, not more numerous. The only fix is to capture it again: fill the frame with the page, and the resolution follows.
How to scan a document without a scanner
The camera is not your problem. A page-filling shot from an ordinary phone carries more detail than most office flatbeds capture at their default setting. What ruins it is the light you shoot in, the angle you hold, and the flash you should not have used.
The short answer. Fill the frame with the page, shoot with light coming from in front of you, and keep the flash off. A page-filling photo from a 12 MP camera works out to roughly 340 DPI across a Letter sheet — comfortably above the 300 DPI most agencies ask for.
The arithmetic, so you can check it yourself
DPI is not a setting on a camera. It is pixels divided by inches. A US Letter page is 8.5 × 11 inches, so at 300 DPI you need 2550 × 3300 pixels — that is 8.4 megapixels.
| Camera | Pixels on a page-filling shot | DPI across a Letter page |
|---|---|---|
| 8 MP | ≈ 2450 × 3260 | ≈ 288 DPI |
| 12 MP | ≈ 3000 × 4000 | ≈ 353 DPI |
| 48 MP | ≈ 6000 × 8000 | ≈ 706 DPI |
Those numbers assume the page fills the frame. That is the whole catch. Shoot the same page from across a desk so it covers a third of the frame, and you keep a ninth of the pixels — a 12 MP camera drops to about 118 DPI, and no software can put the detail back.
The four things that actually go wrong
1. Your own shadow
You lean over the page to line up the shot, and your head and shoulders block the ceiling light. The shadow lands exactly where you are photographing. Put the page next to a window and stand so the light arrives from in front of you, not from behind your back.
2. The flash
A flash fires from a few inches away and lands as a hot circle on the paper. Inside that circle the sensor clips: every pixel reads maximum brightness, so there is no difference left between the ink and the paper. A shadow can be corrected because the letters are still there, only darker. A blown highlight cannot, because nothing was recorded. If a page has a flash hotspot across the text, take it again without flash.
3. The angle
Holding the phone at a tilt turns the rectangle into a trapezoid, and the far edge of the page ends up with fewer pixels per inch than the near edge. Perspective correction straightens this, but it works from the pixels you captured — the far edge stays the softest part. Shoot from directly above where you can.
4. Cropping in the gallery afterwards
Cropping a photo in the phone gallery keeps the pixels but usually re-saves the JPEG, and each re-save costs a little detail on the thin strokes. Crop once, at the end, not repeatedly.
The order that works
- Flat surface, page next to a window, light from in front.
- Phone parallel to the page, page filling the frame, flash off.
- Tap the screen on the text so the camera exposes for the paper.
- Straighten the angle, even out the lighting, then export at the size the portal asks for.
The last step is the one people skip, and it is the one the portal checks.
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