If you've ever been asked to "scan at 300 dpi" and just nodded, you're in good company. The number is the dial between a scan that's crisp and a file that's either blurry or needlessly huge.
Two words get mixed up here. Strictly, dots per inch (dpi) describes scanners and printers, and pixels per inch (ppi) describes a digital image. In everyday use people swap them, and agency rules often use one or the other. This page treats them as the same idea: how many tiny samples of the page fit in one inch.
What a DPI is
Picture a grid laid over a page. At 100 dpi, each inch of paper is cut into 100 squares across and 100 down. At 300 dpi, it's 300 by 300. Each square gets one color, so more squares means finer detail: small print stays legible, thin lines don't smear, a signature looks like a signature.
The catch is size. More squares means more data. Doubling the dpi quadruples the number of pixels, so file sizes climb quickly.
Dpi also depends on the paper. The National Archives' own scanning guidance notes that its dpi figures are meant to be equivalent dpi for the size of the original document.
What it looks like
Here are the numbers that official sources actually give, with the context that makes each one fair to use.
| Situation | What the source says | Source |
|---|---|---|
| Modern text records kept as permanent federal records | Minimum 300 pixels per inch, sized to match the original | National Archives |
| Photographic prints, or paper with fine detail | Minimum 400 ppi, sized to the source; more may be needed | National Archives |
| Passport photo, paper | 2 x 2 inches (51 x 51 mm), high resolution, not blurry, grainy or pixelated | State Department |
| Passport photo, online upload | JPG, PNG, HEIC or HEIF, 54 KB to 10 MB; use the highest quality camera setting | State Department |
| Re-scanning a printed passport photo | Avoid it; it may lower the quality | State Department |
| Cultural-heritage collections (museums, libraries) | Detailed federal guidelines, third edition developed 2022-2023 | FADGI |
Two things stand out. The 300 ppi rule is a minimum for agencies preserving permanent records, not a law for your household paperwork. And for the passport photo, the State Department doesn't state a dpi at all. It cares that the result is sharp. If you want the arithmetic anyway: a 2 x 2 inch photo at 300 pixels per inch is 600 x 600 pixels, and a US Letter page (8.5 x 11 inches) at 300 is 2550 x 3300. That's math, not a requirement.
What to keep and for how long
Dpi isn't a document, so what you keep is the scan itself, at a quality you won't regret later.
- Scan once, at a keeper setting. Re-scanning from a bad scan can't recover detail that was never captured. For papers you'll need for years, such as a lease, a deed or a tax record, use a setting near the 300 ppi reference point.
- Check legibility, not just the number. Zoom to 100% and read the smallest print. If you can read it, the scan is good enough.
- Mind file size. If a portal limits uploads, shrink a copy rather than re-scanning. A PDF compressor can do that while you keep the full-size original.
- Keep the original paper when the rules say to. How long to hold a document depends on what it is; see what documents to keep and for how long and document retention.
For step-by-step scanning on a phone, read how to scan documents on iPhone. For photo requirements, see the passport photo tool and documents needed for a passport. If a photo comes off an iPhone as HEIC, the State Department accepts that format for online renewal.