I am trying to find the actual size of the etherum blockchain.
I just found older posts that says it is around 21GB.
Blockchain size in ethereum depends in the implementation. In Parity is about 6 GB, in Geth is about 11 GB. Geth is not implementing state pruning, so 11 GB would be a clean sync with --light, while if you don't use this would be 60GB+.
For disk space needs, see this answer.