As I understand for BIP32. There are 2048 words.
12 words would give you 2048^12 combinations. However, not all combinations are valid because of the checksum, so how do i calculate the actual space?
BIP 32 is not a mnemonic specification, so it has 0 possible combinations.
I assume you are talking about BIP 39. In that case there are are
2048^12 combinations for 12 word mnemonics,
2048^18 for 18 word mnemonics, and
2048^24 for 24 word mnemonics. However BIP 39 currently supports 8 languages, so there are
(2048^12 + 2048^18 + 2048^24)*8 possible combinations.
The checksum doesn't matter because BIP 39 does not specify that the checksum must be enforced. The checksum can be invalid, and all that BIP 39 compliant software should do is show a warning.