From Plan document versioning:
When you create a new version of a document, the incremental changes are stored in SQL Server, rather than a complete new copy of the document.
In depth, it's handled by Shredded Storage that covers not only versions, but all BLOBs in general.
You might want to take a look at SQL queries in that article and maybe give them a try in your test environment while performing the sample scenario you described.
Practically file versions are stored in increments, however I'd rely on documentation when planning overall farm capacity:
Formula to estimate content database storage
Database size = ((D × V) × S) + (10 KB × (L + (V × D)))
- Calculate the expected number of documents. This value is known as D in the formula.
- Estimate the average size of the documents that you'll be storing. This value is known as S in the formula.
- Estimate the number of list items in the environment. This value is known as L in the formula.
- Determine the approximate number of versions. [...] This value is known as V in the formula.
This estimation formula could be expressed like: Database size = DV × (S + 10 KB) + 10 KB × L (each document version takes full size).