It varies quite a bit. There are two different types of caches: SLC and DRAM. Most drives use SLC caching, higher end drives often use both.
Typically the SSDs with DRAM have a ratio of 1GB DRAM per TB of flash.
SLC caching is using a portion of the flash in SLC mode, where it stores 1 bit per cell rather than the typical 2-4 (2 for MLC, 3 for TLC, 4 for QLC) in exchange for higher performance. SLC cache size varies wildly. Some SSDs allocate a fixed size cache, some allocate it dynamically based on how much free space is available. It can potentially be 10s of GBs on larger SSDs.
Typically the SSDs with DRAM have a ratio of 1GB DRAM per TB of flash.
SLC caching is using a portion of the flash in SLC mode, where it stores 1 bit per cell rather than the typical 2-4 (2 for MLC, 3 for TLC, 4 for QLC) in exchange for higher performance. SLC cache size varies wildly. Some SSDs allocate a fixed size cache, some allocate it dynamically based on how much free space is available. It can potentially be 10s of GBs on larger SSDs.