This site tells the experience needed for a level as well as what your attack dice should be before adding your attack bonus sides to it. Currently there are only 50 levels and it will take long enough to get those.
Lvl 1 - 0 exp - 20 sides
Lvl 2 - 100 exp - 21 sides
Lvl 3 - 200 exp - 22 sides
Lvl 4 - 300 exp - 23 sides
Lvl 5 - 400 exp - 24 sides
Lvl 6 - 900 exp - 25 sides
Lvl 7 - 1400 exp - 26 sides
Lvl 8 - 1900 exp - 27 sides
Lvl 9 - 2400 exp - 28 sides
Lvl 10 - 4000 exp - 29 sides
Lvl 11 - 5000 exp - 30 sides
Lvl 12 - 6000 exp - 31 sides
Lvl 13 - 7000 exp - 32 sides
Lvl 14 - 8000 exp - 33 sides
Lvl 15 - 9000 exp - 34 sides
Lvl 16 - 10000 exp - 35 sides
Lvl 17 - 11000 exp - 36 sides
Lvl 18 - 12000 exp - 37 sides
Lvl 19 - 13000 exp - 38 sides
Lvl 20 - 18000 exp - 39 sides
Lvl 21 - 23000 exp - 40 sides
Lvl 22 - 28000 exp - 41 sides
Lvl 23 - 32000 exp - 42 sides
Lvl 24 - 37000 exp - 43 sides
Lvl 25 - 42000 exp - 44 sides
Lvl 26 - 47000 exp - 45 sides
Lvl 27 - 52000 exp - 46 sides
Lvl 28 - 57000 exp - 47 sides
Lvl 29 - 62000 exp - 48 sides
Lvl 30 - 70000 exp - 49 sides
Lvl 31 - 78000 exp - 50 sides
Lvl 32 - 86000 exp - 51 sides
Lvl 33 - 94000 exp - 52 sides
Lvl 34 - 102000 exp - 53 sides
Lvl 35 - 110000 exp - 54 sides
Lvl 36 - 118000 exp - 55 sides
Lvl 37 - 126000 exp - 56 sides
Lvl 38 - 134000 exp - 57 sides
Lvl 39 - 142000 exp - 58 sides
Lvl 40 - 152000 exp - 59 sides
Lvl 41 - 162000 exp - 60 sides
Lvl 42 - 172000 exp - 61 sides
Lvl 43 - 182000 exp - 62 sides
Lvl 44 - 192000 exp - 63 sides
Lvl 45 - 202000 exp - 64 sides
Lvl 46 - 212000 exp - 65 sides
Lvl 47 - 222000 exp - 66 sides
Lvl 48 - 232000 exp - 67 sides
Lvl 49 - 242000 exp - 68 sides
Lvl 50 - 260000 exp - 70 sides
