btrfs filesytem usage

The basic linux monitor for free disk space returns similar values as running "$ df -h". However this can be misleading if btrfs subvolumes are used. The size of the subvolumes is not included and thus the amount of free space can be much smaller then what the monitor indicates. The real value can be obtained by running "$ btrfs filesystem df /".

Is there any monitor I could use that would work with btrfs?