Does upgrading trello upgrade only the board or the whole account?

[Malak Mohammed Abu Zaid]

Upgrading trello upgrades only the board or the whole account? Also if my board is upgraded, all the members in the board can benefit or they have also to upgrade their accounts?

Thank you

[Michael Pryor]

Business Class upgrades the team including all the boards in that team.  It is paid per user for every member of the team or any guests who are not on the team but are on more than one board. 

https://help.trello.com/article/831-trello-business-class-vs-trello-gold

If you have a board in a Business Class team then anyone on that board can use the features. 

[Nic Brough _Adaptavist_]

It's the whole account, the one that owns the board.

[Malak Mohammed Abu Zaid]

And do the members of the boards benefit even if their accounts are free?