Currently Ceilometer does not provide how many vcpus and total memory is assigned to an instance so it is not possible (without external data) to calculate percentages.

However, those data are provided by libvirt in their domstats for the domain as:

vcpu.current=8

balloon.current=65536000

So it would be great if the Ceilometer agent could provide this data.

This also happens with disks:

block.0.capacity=322122547200