Depends where you are at on your grow if for veg. it can be high. I never went above 60 to 65. As far as for flower you want to keep it on the low side. If the hum. is too high you risk mildew. I never went above 30 to 40. Hope this helps.
Well really it all depends on what stage of growth your plants are at. Clones need a rather high humidity level towards 90%, but Flowering plants need lower levels if they stay high for too long pest can become a big problem.