A general rule ,is to multiply your theoretical worst run of outs by 3.5,if betting level stakes, to work out your bank size.
Remember ,
No Bank = No Chance

Get the bank size wrong & it will be purely luck only, that might save you.

Here are the theoretical worst run of outs you should expect to strike at some stage of your punting career ,depending on your strike rate average.
S/R-Outs in a row
10%-65
15%-42
20%-31
25%-24
30%-20
35%-16
40%-14
45%-12
50%-10
55%-9
60%-8

__________________
Cheers.