Under Construction.
A 32 GB iPhone has about 28 GB available for user data.
If you have 33 apps, the average, they will take 2-3 GB.
In the remaining 25 GB you can get about:
6,000 pictures (12 MP camera)
or 2,500 songs *
or  4 HD movies
or  3 hrs of HD video you record
* Note: Many people prefer to keep their music in the cloud,
  but if you want music while you're not on Wi-FI (e.g. jogging, flying,...)
  you will want to download some music.

  iPhone 5 & 6    8 MP camera	1.5-3.8 MB/photo1
  iPhone 6s & 7  12 MP camera	2.4-5.2 MB/photo

1 Compression varies depending on the amount of detail
  HDR adds about 220K
2 iPhone 6s and above have a live video option which captures a 3 sec. video
 in addition to the photo. It adds 500K to the image size
  iTunes uses Advanced Audio Compression (AAC) (.m4a file extension)
  It is compressed and has an average bit rate of 256 Kbps.
  Popular music av 2.6 MB/min av 3.2 min/song = 8 MB/song
  Classical music av 2.3 MB/min 7-9 min/song = 18 MB/song
 You can tell iTunes to transcode stuff to 128 kbps to reduce the size
   when syncing to iDevices.
Apple ACC at Audio Video

 SD		1-3 GB
 HD 30fps	130MB/min	45 min = 3-6 GB
 HD 60fps	200 MB/min	
 4K 30fps	375 MB/min
 Space will depend on the detail and amount of motion because of the
 way the compression works.
Movies and TV shows take up less space than vido you record.
  HD 2.6 GB/hour - most movies are about 2 hrs so 5 GB
See Final Cut Pro 7 User Manual: Determining How Much Space You Need


iPhone Average 70 MB per app (9.3 GB for 132 apps)
Android Average 72 MB per app (5.96 GB fpr 83 apps)
The largest I had were, Numbers (317 MB) and Facebook (165 MB) on iPhone.
Kindle (220 MB), Excel (206 MB),Chrome (193 MB), Facebook (178 MB) on Android. 25% were > 75 MB; 25% were < 25MB; Median was 38 MB

The average user in the U.S. had 33 apps downloaded.
I have 136 over 2 1/2 years of iPhone use.

Average abut 1.5 - 3 apps/month.
Source: How many mobile apps are downloaded by the average smartphone user each month (by platform)? - Quora

How many apps does the average iPhone user have installed? - Quora
Consumers Spend 85% Of Time On Smartphones In Apps, But Only 5 Apps See Heavy Use | TechCrunch


last updated 1 Oct 2016