An oversized plan wastes money; an undersized one takes the site down. Here is how to size it.
Traffic
Visitor count alone is not a sizing rule. Review cache, request cost, concurrency, database load and background jobs, then scale from observed usage.
Disk
A WordPress blog is roughly 2-5 GB. An image-heavy shop is 10-25 GB. Add room for backups.
Stack
Match the stack against the selected plan's catalog features. Root access, custom daemons and Docker normally require VPS/VDS; confirm exact support before ordering.