I've been looking at designing an RPG system lately and I'm currently considering where to set the "difficulty" of a roll at to get some satisfying results.

I'm wondering - has anyone researched some "average" RPG probabilities that "feel good"? My guess would be having something like a 50% success chance as a baseline, then turning it up to something like 75%, 87.5%, etc. as proficiency goes up seems to at least sound good on paper, but it would be nice to have a comparison to some games out there.

I'd be interested to know what kind of probabilities have a good "game feel" - how difficult ought it to be to succeed at a roll of some task you're new at, something you're proficient at, and something you're a master of for example.

I know that in systems like D&D your to-hit bonuses and enemy defences both scale, and many games like PbtAs have a somewhat static difficulty. I'm wondering if there are any design docs for roll probabilities, or does anyone have their design experience to share on such numbers?


1 Answer 1


Yes, research has been done.

A google search (I used "tabletop rpg design good probabilities") provides a plethora of useful articles, many of which are free.

I found this one by Asher Stevenson in their Wonky & Technical section of Medium.com to be particularly close to what you seem interested in.

I also thought this Reddit post succinctly posits another important fact about die odds... they should vary by system and setting.

If you're looking for guidance on how to meet probability requirements when you've decided the odds that are right for your design, there are also articles about that.


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