What DPI to scan photos: prints, slides and negatives
Scan photo prints at 600 DPI to keep, 300 to reprint at the same size, and film at 3,000 to 4,000. The figures archives use, and the sums behind them.
Published
Scan photo prints at 600 DPI if you want a copy to keep and enlarge, and at 300 DPI if you only need to reprint them at the same size or share them on a screen. Scan 35 mm slides and negatives at 3,000 to 4,000 DPI, because the original is tiny. Going higher on a print mostly makes a bigger file of the same picture.
The 600 and the film figures are not guesses. They are the upper levels the United States federal archives and libraries set for themselves. The 300 is simply the resolution print is judged at, and the arithmetic behind all of them is short enough to do in your head.
The one sum to remember
A scanner’s DPI is the number of samples it takes from each inch of the original. What you do with the scan afterwards decides how much you need:
largest good print = original size × scan DPI ÷ 300
Scan at 300 and you can print at the same size. Scan at 600 and you can print at twice the size, or crop to half the picture and still print the original size. Scan at 1,200 and you can print at four times the size, if the print holds that much detail, which it usually does not.
Photo prints
| Scan at | Pixels | Megapixels | Largest print at 300 DPI | |
|---|---|---|---|---|
| 4 × 6 in | 300 | 1200 × 1800 | 2.2 | 4 × 6 in |
| 4 × 6 in | 600 | 2400 × 3600 | 8.6 | 8 × 12 in |
| 4 × 6 in | 1,200 | 4800 × 7200 | 34.6 | 16 × 24 in |
| 5 × 7 in | 300 | 1500 × 2100 | 3.2 | 5 × 7 in |
| 5 × 7 in | 600 | 3000 × 4200 | 12.6 | 10 × 14 in |
| 8 × 10 in | 300 | 2400 × 3000 | 7.2 | 8 × 10 in |
| 8 × 10 in | 600 | 4800 × 6000 | 28.8 | 16 × 20 in |
A 4 × 6 inch print scanned at 600 DPI is about 25 MB before compression, in 8-bit colour. At 1,200 it is about 99 MB, and a higher setting takes longer to scan.
What the archives use
The Federal Agencies Digital Guidelines Initiative, FADGI, publishes the guidelines that US federal agencies follow when they digitise their collections. Its Technical Guidelines for Digitizing Cultural Heritage Materials, third edition, 2023, grades a scan from one to four stars. For “Prints and Photographs” the resolution for each level is:
| FADGI level | What FADGI says it is for | Prints and photographs |
|---|---|---|
| 1 star | “to provide a reference to locate the original” | 200 ppi |
| 2 star | “the minimally acceptable rating for most professional digitization activity” | 250 ppi |
| 3 star | “a very good professional image that is appropriate for most uses” | 400 ppi |
| 4 star | “the best imaging practical today” | 600 ppi |
A footnote to the 600 figure reads: “In rare cases, resolutions higher than 600 ppi may be needed to resolve fine details.” So the best practice of a national archive for a photographic print is 600, with more only as an exception. That is why 600 is a sound choice at home for anything you care about, and why 1,200 is rarely worth the wait.
FADGI writes ppi, pixels per inch, and notes that “DPI is often used in scanning and image processing software to refer to spatial resolution and this usage is an understandable convention”. The number in your scanner’s DPI box is the same thing.
Resolution is only one of the things those levels measure. The guidelines also set colour accuracy, tone and noise, and they say of photographs that “accurate tone and color reproduction in the scan play an equal, if not more, important role”. A clean 600 DPI scan with the right colours beats a 2,400 DPI scan with the wrong ones.
Slides and negatives
A 35 mm frame is 36 × 24 mm, about 1.4 × 0.9 inches. To make a print from it, the scan must be enlarged many times, so it needs far more samples per inch:
| 35 mm frame scanned at | Pixels | Megapixels | Largest print at 300 DPI |
|---|---|---|---|
| 1,000 DPI | 1417 × 945 | 1.3 | 4.7 × 3.1 in |
| 2,000 DPI | 2835 × 1890 | 5.4 | 9.4 × 6.3 in |
| 3,000 DPI | 4252 × 2835 | 12.1 | 14.2 × 9.4 in |
| 4,000 DPI | 5669 × 3780 | 21.4 | 18.9 × 12.6 in |
FADGI’s levels for film, both transparencies and negatives:
| Film | 1 star | 2 star | 3 star | 4 star |
|---|---|---|---|---|
| 35 mm up to 4 × 5 in | 1,000 ppi | 2,000 ppi | 3,000 ppi | 4,000 ppi |
| 4 × 5 in and larger | 500 ppi | 1,000 ppi | 1,500 ppi | 2,000 ppi |
For a box of family slides, 3,000 to 4,000 DPI gives a file with as many pixels as a 12 to 21 megapixel camera photo. One practical point that is ours, not FADGI’s: film is see-through and has to be lit from behind, so a flatbed scanner can scan it only if its lid has a light made for film. Check the scanner’s manual.
Choosing for your own photos
- Everyday snapshots to share and reprint small: 300 DPI. Quick, and the files are small.
- Photos you want to keep, crop or enlarge: 600 DPI. This is the usual answer.
- Very small prints, such as a passport photo or a locket picture: 1,200 DPI is our suggestion, not a FADGI figure. The reason is the sum above: there are so few inches to sample that a 2 × 2 inch print at 600 is only 1200 × 1200 pixels, enough for a 4 inch print, while at 1,200 it is 2400 × 2400, enough for 8 inches. FADGI’s own allowance is its footnote that more than 600 may be needed “in rare cases”.
- Slides and negatives: 3,000 to 4,000 DPI.
- A print you will only ever look at on a phone: 300 is still enough. A 4 × 6 at 300 is 1200 × 1800 pixels.
If you are unsure, scan one photo at 300, 600 and 1,200, zoom in on a face in each, and stop at the setting where the next one up shows nothing new. Past that point you are recording paper texture and dust.
Settings that matter as much as DPI
- Colour, even for black-and-white prints. FADGI’s note on prints and photographs says master files “from both color and black and white originals are to be imaged in 16-bit color at or above 3-star performance”, because the tone of an old print is part of it. At home, scanning a sepia print in colour keeps the sepia.
- A master and a copy. FADGI’s master formats are TIFF and JPEG 2000. Save the scan once as a TIFF, or as a PNG, and make JPEG copies from it for sharing. A JPEG saved again and again loses a little each time.
- No automatic fixes on the master. FADGI does not allow dust removal or colour restoration on master images: “Adjustments to correct or enhance the image may be made to access versions”. Keep the untouched scan and edit a copy.
- The whole photo. “We recommend the entire object be scanned, without cropping. A small border should be visible around the entire document or photographic image.” Borders carry dates and notes, and you can crop a copy later.
Handle the originals gently
The US National Archives’ advice on digitising family papers and photographs is short:
- Make sure the original fits completely on the scanner glass. “The lid of the scanner can crush and crease the original if the paper doesn’t fit on the scanner.”
- Automatic feed scanners “are not suitable for fragile, weak, bent, or valuable papers”, which “can jam and become torn”.
- “Keep your originals after you digitize them, because digital files have their own preservation risks and can easily be lost.”
- Back up: “Three copies, stored on two different media, and one copy located off-site.”
FADGI adds that glass may be used to hold a photograph flat “only when the original will not be harmed by doing so”, and that “tightly curled materials must not be forced to lay flat”. A curled or cracked old print is a job for a camera on a copy stand, or for a conservator, not for a scanner lid.
Clean the glass before you start. FADGI warns that on a flatbed “dust and dirt on the scanner glass and optical system can result in dust and dirt in the file”.
Check what you got
Open a finished scan in the image DPI checker. It shows the pixel size, the DPI the scanner wrote into the file and the size it prints at 300. If the pixels are right and the stored DPI is not, the DPI converter corrects the stored value without touching the picture.
To see what a scan of a given size comes to, the size tables do the sum: 4 × 6 inches at 600 DPI, or 600 vs 1200 DPI for when the higher figure is worth it.
Questions
Is 1,200 DPI better than 600 for photos? It makes a file four times the size. FADGI’s top level for photographic prints is 600, with higher resolutions only “in rare cases”. For a very small original that you mean to enlarge, 1,200 is a reasonable choice, by the sum above.
What DPI for old photos? The same: 600. Age does not add detail, though it is a reason to scan in colour and to handle the print with care.
What DPI to scan photos for a photo book? 300 if the picture goes in at its original size or smaller, 600 if it will be enlarged or cropped.
What about documents? Text needs less. See what DPI to scan documents.