It depends on how many chips you are playing on each spin. let's say your'e betting 3 chips each spin (one chip on each number)then you divide 36/3 =12 That mean you can recoup your losses if you lost 11 spins and won on the 12th. If you lose all 12 spins then you wanna start another progression.Which is gonna be double the chips amount but half of the number of spins. so we play 6 chips (2 chips per each number) for 6 spins . If you lose 5 spins and you win on the 6th then you recoup all your previous losses on the 17 spins. If you lose all 6 spins then you start another progression playing 12 chips on 3 numbers each number is covered with 4 chips, you bet for 6 spins ,if you lose 5 spins and win on the 6th you recoup all previous loses from all 24.

If you reach to that point then it is not your day!

But usually if you have a good skill or strategy you should at least hit 1 in 24 spins. and thats all what you need.

Good Luck!