It is important to keep in mind that hardly any of the studies and experiments that established "correct" dosage for things like penicillin or ibuprofen have been published regarding cannabis. We know that in the laboratory, so far mostly with rodent models, CBD modulates the biological systems that are involved in inflammation, including autoimmune inflammation like RA. We also know that CBD appears remarkably non-toxic and safe to use, and that patients with RA and similar conditions have reported it helpful. That is folk-medicine knowledge, and when folk-medicine gets validated using science it becomes possible to discuss the "correct" doses for specific conditions. The role of CBD, THC and the other cannabinoids in conditions like RA is still being investigated and we are a long way from establishing "correct" doses. Most patients wanting to try CBD will start around 20mg a day and work up, but please remember that, depending on the preparation, ingested (rather than inhaled) CBD is not completely bioavailable, meaning how much you absorb and goes into your system may be different from what you are taking. Because no harmful amount of CBD has yet been identified there is no guidance for how much to use except common sense, or the development of adverse symptoms like nausea or diarrhea. I assume you are also taking prescription medication for your RA; I would definitely advise reviewing any change in your treatment plan, including CBD, with your rheumatologist.