How many BTC addresses have balance in them? Of all the possible BTC addresses, how many have balance in them?
And what percentage of the total possible addresses is that?
There are approximately 800,000 unique addresses on the blockchain with some Bitcoin held at those addresses at the present time according to blockchain.com.
Let's assume these addresses are all bech32 (to simplify the calculation, in reality these are the minority).
The witness program in a bech32 SegWit v0 P2WSH address is 32 bytes. In theory this means there could be approximately 8^32 = 7.9 x 10^28 different witness programs.
The percentage of unique addresses on the blockchain then works out to be:
800,000 / 7.9 x 10^28 = 1.0 x 10 ^(-23)
This is 0.00000000000000000000001 percent of the total bech32 SegWit v0 addresses.