It is a pain to try to compare stuff though because there aren't good standards for "cloud revenue." According to [1] IBM generated $18.5B over 12 months in cloud revenue. While Forbes[2] talks about $6.1B and $6.9B in quarterly cloud revenue of Amazon and Microsoft (a $24 - $28B annual run rate), and this from Forbes[3] in April of this year that has them at $44B(Amazon), $19B (Microsoft), and $17B (Google). Which would make Google #4 if IBM's numbers hold up under scrutiny.
I try to keep an eye on these numbers to maintain a sense of the shifting landscape, and it doesn't seem like Google has yet found the right combination of goods and services to really be solid in this space yet.
[1] https://www.lightreading.com/enterprise-cloud/infrastructure...
[2] https://www.forbes.com/sites/bobevans1/2018/08/03/1-microsof...
[3] https://www.forbes.com/sites/johnkoetsier/2018/04/30/cloud-r...