Photo Scan Storage Calculator

Why old photos turn into a storage project

That shoebox of family prints looks small on the shelf, but the moment you start scanning it, every photo becomes a multi-megabyte file - and a few hundred scans quietly add up to tens of gigabytes. The surprise is that the file size is almost entirely in your control: the DPI you choose, the color depth, and the file format decide whether one photo costs you 2 MB or 300 MB. Most people either scan everything at maximum quality and drown in terabytes, or scan too small and end up with files that look soft when reprinted. A quick estimate before you start saves both the disk space and the re-scanning.

How the storage math works

A scan's pixel count is simple multiplication: the print's width and height in inches, each multiplied by the DPI. A 4x6 inch print at 600 DPI becomes 2,400 x 3,600 pixels - about 8.6 megapixels. Multiply those pixels by the bytes each pixel needs (3 for standard 24-bit color, 6 for 48-bit archival color, 1 for 8-bit grayscale) and you get the raw size. The file format then shrinks it: uncompressed TIFF keeps everything, compressed TIFF roughly halves it, PNG saves about 40 percent, and high-quality JPEG keeps roughly a quarter - at the cost of some editing headroom. Multiply the per-scan size by your photo count and you have the project's total.

Worked example

Say you have 200 family prints, all 4x6 inches, and you scan them at 600 DPI in 24-bit color as uncompressed TIFFs. Each scan is 24.7 MB, so the whole batch needs about 4.8 GB. At 2 minutes per photo on a flatbed scanner, that is roughly 6.7 hours of scanning - basically a full weekend afternoon. A 500 GB external drive holds this project easily, with about 495.2 GB to spare - in fact it could hold about 20,712 photos at these settings. But push the same 200 prints to 8x10 size at 1200 DPI and each scan balloons to 329.6 MB; 500 of those would need 160.9 GB. That is why the DPI decision matters more than anything else.

Practical tips

For standard prints, 600 DPI is the sweet spot - it captures all the detail the paper holds, and going to 1200 DPI on a 4x6 mostly just quadruples the file. Reserve 1200 DPI and up for small originals like 35mm negatives and slides, where you need the extra resolution to enlarge. Scan irreplaceable photos as TIFF (48-bit if your scanner supports it) and keep a JPEG copy for sharing; you can always make a small file from a big one, never the reverse. Name files with dates and people as you go - a "scan now, organize later" pile becomes a second project. And budget the time honestly: two minutes per scan sounds fast until you multiply it by a thousand.