Is it normal for cloud server

Hi,

I'm never really using any cloud server on the market...

and with recent offer from Google and AWS,signed up and got the promo credit... for AWS I'm using it only for my Glacier since EC2 is too much to compare with promo credit received(micro instance about $18 a month)...

so,now I'm using Google Compute Engine with the promo $1000....launching micro instance for almost two months now,left idle...weirdly enough for me when seeing the charge/usage...my actual disk usage is less than 1GB,or about 700MB default install Debian 7...but shown in billing is about 5GB and being charged for it...

df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs           10G  734M  8.8G   8% /
/dev/root        10G  734M  8.8G   8% /
none            296M     0  296M   0% /dev
tmpfs            60M  112K   60M   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           119M     0  119M   0% /run/shm

Nov 1 - Nov 30  
Google Compute Storage Pd Capacity: 5.68 GB-month (Project:xxxxxxxxxxxxx)
    0.57    

I'm sorry if it's just me not knowing much about how cloud being charged...really appreciate if anyone can get me to better understand...