If you are talking about NewTon full node then initial size after sync would be around 20G but it will steadily grow, reserve at least 10x of that if you wish to sleep quietly. Nice way to save on space in hosting environment is by using compressable FS such as ZFS, it works like a charm, performance is not affected or even improved.
You also need to pay attention to your limits on open files, if your OS places such limits you’d need to increase to about 200k or remove them entirely. This is due to RocksDB.
For statistics, our archival nodes take up around 1TB of space and keep over 140k open files.