Every offline photo app dodges this question. Here are the real numbers from a real library — 190,566 photos across two external drives — measured on the phone that carries them.
CachePix does not copy your photos to your phone. It syncs a thumbnail for every photo in your library, and that thumbnail set is what makes the whole archive browsable and searchable offline. On the library measured below, that came to 8.03 GB for 190,566 photos — about 44 KB each, and under 1% of the 885.66 GB the originals occupy.
Two folders on one external drive, catalogued by the CachePix desktop app on a Mac and synced to an iPhone over local Wi-Fi.
| Source folder | Size | Items |
|---|---|---|
| Sports | 817.97 GB | 185,240 |
| Travel | 67.69 GB | 12,397 |
| Total | 885.66 GB | 197,637 |
| Photos catalogued by CachePix | — | 190,566 |
| On the phone | Size | Covers | Optional? |
|---|---|---|---|
| Thumbnails | 8.03 GB | Whole library — all 190,566 photos | Always present |
| HD previews | 63.46 GB | Set to All photos — the maximum | Optional, removable |
Both numbers are real, and the second one deserves an explanation rather than a footnote. 63.46 GB is what you get when you set HD previews to every photo in a 190,566-photo archive — the highest setting the app offers, chosen deliberately. It is not the default, it is not required to browse anything, and a single Free Up Space tap in the Sync tab removes all of it. Thumbnails stay, so the whole library stays browsable.
| Thumbnails | HD previews | |
|---|---|---|
| Purpose | Browse, scroll, and search your entire library offline | Open an individual photo sharp with no network at all |
| Coverage | Every photo, always | Only what you choose |
| Measured average | ~44 KB per photo | ~349 KB per photo |
| Removable | No — they are the catalog | Yes, one tap |
| Without it you can still… | — | Browse everything, and fetch any photo in HD on demand over Wi-Fi |
Scaled from the measured averages above. Your own figures will vary with image dimensions and subject matter, but the shape holds: the whole-library thumbnail set is a small fraction of a modern phone.
| Library size | Thumbnails (whole library) | If you also set HD previews to every photo |
|---|---|---|
| 10,000 photos | ~0.4 GB | ~3.3 GB |
| 25,000 photos | ~1.1 GB | ~8.3 GB |
| 50,000 photos | ~2.1 GB | ~16.6 GB |
| 100,000 photos | ~4.2 GB | ~33 GB |
| 190,566 photos | 8.03 GB (measured) | 63.46 GB (measured) |
Everything is in the phone app, not buried on the desktop. Open the Sync tab:
Changes apply on the next sync. Nothing is ever deleted from your drives — CachePix only reads them.
Cloud photo services solve this problem by storing your full-size originals on their servers and charging you by the gigabyte, forever, for the privilege. An 885 GB library needs a multi-terabyte plan and a permanent monthly bill. CachePix takes the opposite approach: the originals stay on the drive you already paid for, and only a lightweight index travels — to your phone, over your own Wi-Fi, at a flat price that does not care how big your archive gets. See pricing.
No. CachePix never copies your original photos to the phone. It syncs a thumbnail for every photo — that is the 8.03 GB figure — and fetches a full-resolution preview on demand when you open an individual photo on your Wi-Fi.
Yes. The Sync tab has a Free Up Space button that removes every HD preview in one tap. Thumbnails always stay, so your whole library remains browsable and searchable afterwards.
If your phone and computer are on the same Wi-Fi, the viewer fetches the full-resolution preview on demand. If you are away from home, you still see the thumbnail and all of the photo's details — filename, folder, date, keywords.
No. It reads your files to build the catalog. It never moves, renames, edits, or deletes an original, and removing a drive from the catalog leaves every file exactly where it is.
Figures measured on a production CachePix install in August 2026 — a 190,566-photo catalog on macOS synced to an iPhone. Per-photo averages vary with image dimensions. Related: external-drive photos on your phone.