# Finer than 5% granularity on a 20-sided die

As a byproduct of the previous project, but perhaps useful on its own, here is a table of all the specific percentages you can get if you add advantage and disadvantage to a d20 roll.

Percent chance Die expression
0.25% 1/20 with advantage
1% 2/20 with advantage
2.25% 3/20 with advantage
4% 4/20 with advantage
5% 1/20
6.25% 5/20 with advantage
9% 6/20 with advantage
9.75% 1/20 with disadvantage
10% 2/20
12.25% 7/20 with advantage
15% 3/20
16% 8/20 with advantage
19% 2/20 with disadvantage
20% 4/20
20.25% 9/20 with advantage
25% 5/20
27.75% 3/20 with disadvantage
30% 6/20
30.25% 11/20 with advantage
35% 7/20
36% 4/20 with disadvantage
40% 8/20
42.25% 13/20 with advantage
43.75% 5/20 with disadvantage
45% 9/20
49% 14/20 with advantage
50% 10/20
51% 6/20 with disadvantage
55% 11/20
56.25% 15/20 with advantage
57.75% 7/20 with disadvantage
60% 12/20
64% 8/20 with disadvantage
65% 13/20
69.75% 9/20 with disadvantage
70% 14/20
72.25% 17/20 with advantage
75% 15/20
79.75% 11/20 with disadvantage
80% 16/20
81% 18/20 with advantage
84% 12/20 with disadvantage
85% 17/20
87.75% 13/20 with disadvantage
90% 18/20
90.25% 19/20 with advantage
91% 14/20 with disadvantage
93.75% 15/20 with disadvantage
95% 19/20
96% 16/20 with disadvantage
97.75% 17/20 with disadvantage
99% 18/20 with disadvantage
99.75% 19/20 with disadvantage
100% 20/20

Not saying use this always (it’s cumbersome af that the target number jumps up and down) but can sometimes (rarely, admittedly) be useful when you’re looking to port over a specific probability from some other system and want to leverage their playtesting. (If you have reason to suspect that a particular rule is not well playtested, then of course you don’t need to approximate their probability either. Just use what would make sense in your game instead.)