How to determine the amount of app space available?

Question

I have recently experienced the "Can't install app in default location" error (code -20), despite 700 MB still free on my phone (no SD card present). Having googled and read, I now know that not all memory can be used to install apps. So while I have some space available, the app-partition (?) space may be up.

But I've never encountered any partitions on my phone. So the question is: how can I determine how much space I have on my phone for the apps?

I use Samsung Note 2, Android 4.4.2. df output (using Terminal Emulator; please note that by now I have already uninstalled several apps, so the available space might have increased. I still don't know how to see it in this listing):

/mnt/secure/asec: Permission denied
/mnt/shell/container: Permission denied
/mnt/shell/emulated: Permission denied
Filesystem                   Size     Used     Free   Blksize
/dev                       892.5M   140.0K   892.3M      4.0K
/mnt/secure                892.5M     0.0K   892.5M      4.0K
/mnt/asec                  892.5M     0.0K   892.5M      4.0K
/mnt/obb                   892.5M     0.0K   892.5M      4.0K
/system                      2.0G     1.7G   253.6M      4.0K
/efs                        19.7M     9.5M    10.2M      4.0K
/cache                       1.3G    21.9M     1.3G      4.0K
/preload                   551.2M   141.9M   409.3M      4.0K
/data                       10.5G     9.8G   702.1M      4.0K
/storage/emulated          892.5M     0.0K   892.5M      4.0K
/storage/emulated/0         10.4G     9.8G   682.1M      4.0K
/storage/emulated/legacy    10.4G     9.8G   682.1M      4.0K

Answer 1

It's your /data partition running low on free space (as always when this error occurs – see our insufficient-memory tag-wiki for details, first-aid and further information). According to the output you've provided, only 700 MB out of 10 GB are available. The "storage low" error is triggered when free space here reaches 10%.

This limitation was introduced to keep a "safety margin" for the system. So the user gets a warning when it was exceeded. In this state, of course Google Play Store refuses to install any new app, as it considers the system alreading running "low on space" and doesn't want to "worsen the situation".

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^{When the 10% rule was introduced, devices came with much less internal storage, so it was quite reasonable (think of those devices with less than 512 MB). Nowadays, it does no longer seem a good idea – especially with MTP being introduced to have the "internal storage" and "internal SD card" on one partition, spanning multiple Gigabytes. Looks like this is an issue not yet addressed or "simply forgotten".}