Some notes on quick game system conversions when all you have is one six-sided die. Roll 1d6, a result equal to or greater than the number shown is a success.
GENERAL MODIFIERS
* +1 to roll … Easy
* +0 to roll … Moderate
* -1 to roll … Hard
* -2 to roll … Very Hard
* -5 to roll … Extreme
d6 ROLL
* Very Easy … roll 2 to 6
* Easy … roll 3 to 6
* Moderate … roll 4 to 6
* Hard … roll 5 to 6
* Very Hard … roll a 6
* Extreme … roll 7 or more (after modifiers)
PERCENTAGE CHANCE (Call of Cthulhu)
* 1% to 17% … roll a 6
* 16% to 33% … roll 5 or 6
* 34% to 50% … roll 4 to 6
* 51% to 67% … roll 3 to 6
* 68% to 83% … roll 2 to 6
* 84% to 100% … roll 1 to 6
d20 ROLL HIGH (AD&D THAC0, B/X Saves)
* 17 to 20 … roll a 6
* 14 to 16 … roll 5 or 6
* 11 to 13 … roll 4 to 6
* 7 to 10 … roll 3 to 6
* 4 to 6 … roll 2 to 6
* 1 to 3 … roll 1 to 6
B/X MONSTER HIT DICE
* HD 1 to 3 … roll a 6
* HD 4 to 6 … roll a 5 or 6
* HD 7 to 11 … roll 4 to 6
* HD 12 to 19 … roll 3 to 6
* HD 20 or more … roll 2 to 6
…or attack versus unarmored (AC 9/10)
* HD 1 to 3 … roll a 4 to 6
* HD 4 to 6 … roll a 3 or 6
* HD 7 to 11 … roll 2 to 6
* HD 12 to 19 … roll 1 to 6
* HD 20 or more … roll 0 to 6
Could also roughly work for character level in place of Hit Dice here.
* Level 1 to 3 … roll a 4 to 6
* Level 4 to 6 … roll a 3 or 6
* Level 7 to 11 … roll 2 to 6
* Level 12 to 19 … roll 1 to 6
* Level 20 or more … roll 0 to 6
…or as modifiers per B/X:
* Level 1 to 3 … +0 to roll
* Level 4 to 6 … +1 to roll
* Level 7 to 11 … +2 to roll
* Level 12 to 19 … +3 to roll
* Level 20 or more … +4 to roll
3d6 OR UNDER (B/X, GURPS)
* 7 or less … roll a 6
* 8 … roll 5 or 6
* 9 or 10 … roll 4 to 6
* 11 … roll 3 to 6
* 12 or 13 … 2 to 6
* 14 or more … 1 to 6
…or less accurate match but more gameable
* 6 or less … roll 6
* 7 to 8 … roll 5 to 6
* 9 to 10 … roll 4 to 6
* 11 to 12 … roll 3 to 6
* 13 to 14 … roll 2 to 6
* 15 or more … roll 1 to 6
PERCENTAGE CHANCE
* 1% to 17% … roll a 6
* 16% to 33% … roll 5 or 6
* 34% to 50% … roll 4 to 6
* 51% to 67% … roll 3 to 6
* 68% to 83% … roll 2 to 6
* 84% to 100% … roll 1 to 6
2d6 ROLL HIGH (Traveller)
* 8+ / no skill … roll 4 to 6
* 8+ / skill 1 … roll 3 to 6
* 8+ / skill 2 to 3 … roll 2 to 6
* 8+ / skill 4 to 5 … roll 1 to 6
* 8+ / skill 6 or more … roll 0 to 6
#d10, 7+ = SUCCESS (WORLD OF DARKNESS)
* 1 die … 4 to 6
* 2 to 3 dice … 2 to 6
* 4 dice … 1 to 6
* 5 or more dice … 0 to 6