This is not a performance benchmark
Framework efficiency, caching, database indexes, cron jobs, imports and traffic spikes can dominate the final requirement.
VPS calculator
Estimate a sensible VPS starting point.
Use workload type, traffic, concurrency and data footprint to get a planning baseline for vCPU, RAM and disk.
Result
Calculated values
Resize from real metrics
Start with a sane baseline and use CPU, memory, I/O, latency and database measurements after deployment.
Leave working room
The disk estimate includes room beyond current application data, but backups should still live independently.
Visits are not equal
Ten thousand cached static page views and ten thousand uncached ecommerce checkouts are very different workloads.