The length of bitcoin address is 34 characters and that includes letters and numbers. So to calculate total number of addresses possible using combination formula:
24- Upper case letters from A to Z, 24- Lower case letters from A to Z, and 10 numbers.
Total number of bitcoin addresses possible are: 58^34 = approx 9 x 10^59 addresses.
That's approximately equal to Novemdecillion possible combinations according to US scale of numbers.
To put things in little perspective, assuming there are 6 Billion people on earth ,then each person can own 9x 10^59 divide by 10^9 = 9 x 10^50 bitcoin addresses.
In other words, each person on this planet can own Sexdecillion bitcoin addresses. That's more than total number of sand grains in the entire planet earth. To conclude we will never really run out of unique bitcoin addresses to use!!
Thanks for reading, until next time :)