I think people have been answering a question that is different from what you are asking.
It looks to me like you are asking something to the effect: *After* upgrading to Postgres 10 - will I use more disk space than 9.5?
I don't believe that there have been significant changes in storage space allocation between 9.5 and 10, so your tables should be the same size. e.g I frequently create a database using pgbench scale 100. it has used 1.5 GB of disk for all the version of Postgres that I have used (and that is quite a few)!
On moving from postgres 9.5.4 to postgres 10.x we have to do data migration.
Can some one let me know will the disk space requirement remain same for same set of tables with same number of rows in postgres 10.x and postgres 9.5.4 ?