What the numbers behind this are
Every estimate here is a stated assumption, not a measurement of your phone. Where Apple publishes a figure, it is Apple's, and linked:
- HEIC, 2.0 MB. Apple's default format since iOS 11. A 12 MP HEIC frame usually lands between 1.5 and 2.5 MB — roughly half what the same shot costs as JPEG.
- JPEG, 4.0 MB. What you get if you set Camera to “Most Compatible”, and what most photos saved from other apps arrive as.
- ProRAW, 25 MB. Apple puts a 12 MP ProRAW file at about 25 MB and a 48 MP one at about 75 MB — ten to twelve times a HEIF frame (About Apple ProRAW). If you shoot at full resolution, triple the result.
- Live Photo, +1.8 MB. A Live Photo stores about three seconds of video beside the still. That video is why a library of Live Photos is far heavier than its photo count suggests.
Videos are deliberately left out. A minute of 4K/60 video costs about as much as 200 HEIC photos, so a handful of long clips will dominate any estimate and make the photo maths meaningless. Your own rate is printed in Settings › Camera › Record Video — Apple shows the MB per minute for the mode you picked.
The only number that is really yours
Open Settings › General › iPhone Storage and read the Photos row. Then open Photos and scroll to the bottom of your library, where iOS prints the item count. Divide the first by the second and you have your true average — no estimate can beat it.
If your real average is far above 2 MB, the usual reasons are Live Photo, bursts (each frame is a full file), and video mixed into the count.
What makes a library big
Photo count alone is a poor guide, because four things quietly multiply it:
- Bursts. Holding the shutter for two seconds can write ten full-size files. They count as ten photos and cost like ten photos, and you will keep one.
- Live Photo. Three seconds of video attached to every still, on by default.
- Saved from apps. Every image forwarded to you in a messaging app can land in your library as a full file you never chose.
- Video. A single 4K clip outweighs hundreds of stills, so a few long videos can dominate the whole number.
This is why two people with 20,000 photos each can be 40 GB apart.
How much of it can actually go?
There is no honest single percentage, and any site quoting one is guessing. What is safe to say is where the weight sits: near-duplicate bursts (ten frames of one moment), screenshots, photos saved from messaging apps, and a small number of very large videos. Those four categories are where a large library's dead weight lives — which is exactly what Kept sorts, on the phone, with every delete recoverable for 30 days.