This query converts the size and free space to GB, then calculate the percent full for the disk.
+-----------+------------------+-------------+-----------------+-----------+--------+
| device_id | description | file_system | free_space (GB) | size (GB) | %_free |
+-----------+------------------+-------------+-----------------+-----------+--------+
| C: | Local Fixed Disk | NTFS | 0.94 | 7.43 | 12.65 |
+-----------+------------------+-------------+-----------------+-----------+--------+
select device_id,description,file_system,
printf("%.2f", free_space/8589934592.0) as 'free_space (GB)',
printf("%.2f", size/8589934592.0) as 'size (GB)',
printf("%.2f", (printf("%.2f", free_space/8589934592.0)/printf("%.2f", size/8589934592.0))*100) as '%_free'
from logical_drives
where size != '-1';
