You can calculate spine-leaf capacity before buying hardware.
Example: Leaves have server ports and uplinks. Spines have ports.
Maximum leaves: (limited by spine ports)
Maximum servers:
Oversubscription: ports at Gbps = Gbps down. uplinks at Gbps = Gbps up. Ratio is :.
A : ratio means non-blocking bandwidth. Every server transmits at full speed. Most data centers accept : or : for cost efficiency.