The short answer, and the arithmetic behind it
A photo from the main camera on a recent iPhone is 12 megapixels, saved in Apple’s HEIC (High Efficiency) format. In everyday shooting those files land at roughly 2–3 MB each — less for a flat, simple scene like a wall or a document, more for a detailed one like leaves, a crowd or a night shot, because compression has more to describe.
Multiply that out and the answer is unglamorous but useful:
- 20,000 × 2 MB = 40 GB
- 20,000 × 3 MB = 60 GB
So a 20,000-photo library sits somewhere around 40–60 GB — before you count a single video. On a 128 GB iPhone that is roughly a third to half the entire phone, which is exactly why a camera roll that size starts triggering storage warnings. (Phone makers count 1 GB as 1,000 MB, and so does this page.)
Same count, very different weight
The per-photo figure moves a lot depending on what you shoot and which settings you use. The table below applies the same 20,000-item count to the common cases:
| What it is | Typical size each | ×20,000 |
|---|---|---|
| Screenshot | ~0.2–0.5 MB | ~4–10 GB |
| 12 MP HEIC photo | ~2–3 MB | ~40–60 GB |
| 12 MP Live Photo | roughly double a still | ~80–120 GB |
| JPEG (“Most Compatible”) | roughly double HEIC | ~80–120 GB |
| 48 MP HEIF (Pro models) | several times a 12 MP shot | more than most phones hold |
| ProRAW | tens of MB | far more than any iPhone holds |
Three of those deserve a note. A Live Photo is a still plus a short video clip, so it costs you roughly twice a plain photo — which is why turning Live off for everyday snaps is one of the quietest storage savings available. JPEG shows up if you set Settings › Camera › Formats to Most Compatible; High Efficiency exists precisely to halve that. And ProRAW, on Pro models, is a professional format whose whole point is keeping data the other formats throw away — wonderful for editing, ruinous for a phone left on it by accident.
One video outweighs hundreds of photos
Here is where most people’s intuition fails. iOS actually prints the cost of video on the screen where you pick the format: open Settings › Camera › Record Video and each option is listed with its size per minute. On a current iPhone that reads roughly like this:
| Recording setting | Per minute | Per 10 minutes |
|---|---|---|
| 1080p HD, 30 fps | ~65 MB | ~0.65 GB |
| 1080p HD, 60 fps | ~100 MB | ~1 GB |
| 4K, 30 fps | ~190 MB | ~1.9 GB |
| 4K, 60 fps | ~440 MB | ~4.4 GB |
Read the numbers on your own phone — that screen is the authority, and the figures shift a little between models and iOS versions. But the shape of it never changes: a single ten-minute 4K clip is about 1.9 GB, which is what 700–900 photos cost. A school concert, a wedding speech and three long birthday clips can outweigh every photo you took that year.
This is the most useful thing to know before a cleanup. If your library is 20,000 photos and 400 videos, the videos may well be the larger half. Finding the heaviest videos is usually the fastest gigabytes you will ever reclaim.
Find your own number in two minutes
Averages are a starting point; your library has an exact answer. Two places give it to you:
- The total. Settings › General › iPhone Storage, then tap the Photos row. That is what your library actually weighs on this phone right now.
- The count. In Photos › Library › All Photos, scroll to the very bottom of the grid. iOS prints a line like “20,013 Photos, 512 Videos”.
Divide the first by the second and you have your real average per item — far better than anyone’s table. Want a single file’s size? Open a photo and swipe up (or tap the info button); the info card shows the format and dimensions, and on recent iOS versions the file size too.
If your figure comes out much higher than the math above, the usual culprits are videos mixed into the count, Live Photos, edited photos — iOS keeps the untouched original alongside your edit so you can revert, which costs space twice — and a Recently Deleted album you haven’t emptied, because deleted items keep their space for up to 30 days.
Count or weight — which is your problem?
Two libraries of 20,000 photos can need completely different cleanups.
If your average per item is small and the total is modest, you have a count problem: thousands of screenshots, saved memes, near-identical tries. Space isn’t really the issue — finding anything is. The fix is thinning by category.
If the total is large but the count is ordinary, you have a weight problem: long 4K videos, screen recordings, ProRAW, big attachments. The fix is a handful of decisions about a handful of very large files, and it can free 20 GB in ten minutes.
Most phones are a bit of both, but knowing which one dominates tells you where to start — and stops you scrolling through five years of photos when four videos were the whole story.
What actually brings the number down
Only two things reduce a library’s real size: deleting items, and shooting fewer or lighter ones. Everything else moves the weight around. Optimize iPhone Storage, for instance, keeps full-resolution originals in iCloud and lighter copies on the phone — that can rescue the device figure while your library, and your iCloud plan, stay exactly as large. It’s worth turning on, but it isn’t a cleanup; see iCloud storage vs iPhone storage for which bucket is actually squeezed.
And the space doesn’t return the instant you delete. Items sit in Photos › Albums › Recently Deleted for 30 days, still taking up room, until that album empties on its own or you clear it yourself. That 30-day window is also your safety net, so empty it only when you’re sure.
Practically, the biggest wins come in this order: the heaviest videos first, then screen recordings, then screenshots and photos saved from other apps, then the near-duplicate runs where you took nine shots of the same thing. That last category is where a 20,000-photo library is often hiding a 12,000-photo library — and it’s the one nobody gets through by hand, because the work isn’t deleting, it’s deciding.
Kept exists for that part. It reads your library on the iPhone — nothing is uploaded, there’s no account — groups the near-duplicates and blurry frames, surfaces the big forgotten videos, and shows you one decision at a time instead of a wall of thumbnails. It tells you how much space a pile is worth before you start, so you can see whether it’s a gigabyte or twenty. Every delete goes to Recently Deleted, reversible for 30 days. Cleaning by hand is free — up to 100 photos a day, every day. Pro is optional: it does the finding and sorting for you, with the price shown on the App Store before you pay.