understanding capacity remaining for disk space

Hi all,

I am wondering how disk space capacity is calcultated in vC OPS5.7.

I have a cluster with 4 datastores on a SAN / 40 VMs :

4.2 To disk space available (Capacity Risk Details view)

3.2 To disk space provisioned by the VMs (Datastore Inventory view)

26 % disk space used

If I put the allocation overcommit ratio for disk space to 0%, I thought it would tell me : a few VMs remaining (no buffer set on disk space)

But it tells me that I am over by 20 VMs ...

Can someone know how does it calculate disk space capacity ?

thanks,

vinny