Calculating the size of /

[Jim Byrnes]

In another thread I was trying to calculate how much disk space to 
allocate to / if I did a fresh install and this time setup  a separate 
/home partition.

To get an idea of how much was outside of the home folder on my present 
install I did:

sudo du -shc /  =>  105GB
du -shc /home   =>  64GB

This led me to believe I had 105GB - 64GB = 41GB that would be in /.

Colin suggested I run Disk Usage Analyzer:

Total filesystem capacity: 264.7GB(used: 104.5GB avail: 160.2GB

/		100%		75.3GB
home		84.1%		63.3GB
usr		6.7%		5.0GB
var		5.8%		4.4GB
lib		2.1%		1.6GB
opt		1.0%		762.2MB
boot		0.3%		194.6MB

Everything else was 0.0%

So this seems to say that if I had a separate /home on this machine that 
/ would be 12GB not the 41GB calculated above.

So what accounts for the difference of 29.2GB between the used of 
104.5GB and / of 75.3GB?

The 12GB and 29.2GB = the 41GB I originally calculated would be needed 
for /.  12GB seems to be more in line with what others reported as the 
size needed for /.

Regards,  Jim