Print DPI & Size Calculator
Switch between checking the print size a scan supports and finding the scan resolution needed to hit a target print size, in inches and centimetres.
Print size
Pixels, DPI, and physical size
A raster scan has no inherent physical size — it's a grid of pixels. DPI (dots per inch) is the bridge between that pixel grid and a real-world print: physical size in inches is simply pixel count divided by DPI. Choosing a higher DPI for the same pixel count shrinks the print; choosing a lower DPI enlarges it, at the cost of visible softness once you go far enough below your scanner's true optical resolution.
For digitizing archival material, it's often more useful to work backward: decide the largest size you might ever want to print an image, and scan at a resolution that supports it now, before the fragile original degrades further.
Frequently Asked Questions
What DPI should I scan an antique photograph at?
For general archiving, 300–600 DPI is a common working range; for small cased images like daguerreotypes and tintypes, many archivists scan at 1200 DPI or higher so the file still supports a reasonable enlargement despite the tiny original. Higher resolution costs more storage and scan time but preserves more detail for future printing or study.
Why does a small original need a much higher DPI to enlarge well?
Print size is simply pixel count divided by DPI, so a small original has fewer physical inches to spread its pixels across even before enlarging. A 2x3 inch tintype scanned at 300 DPI yields only 600x900 pixels — enough for a same-size print but not much more. Scanning that same plate at 1200 DPI instead yields 2400x3600 pixels, giving you the resolution headroom to print larger later.
Does a higher DPI scan always look better?
Only up to the point where the scanner is actually resolving more real detail from the source. Beyond your scanner's optical resolution, a higher DPI setting mostly just interpolates and inflates file size without adding genuine sharpness. Check your scanner's rated optical (not just interpolated) resolution before choosing a very high DPI.
What DPI is 'archival quality' for these processes?
There's no single universal number, but many institutional guidelines for photographic materials recommend scanning at 300–600 DPI at the original's true size for standard prints, and considerably higher for small-format originals such as cased images, so the digital file remains useful well beyond the current project.
Educational tool only. Actual print quality also depends on your scanner's true optical resolution, the source material's condition, and your printer — treat these figures as planning estimates.