If you don’t know about the American Wood Council’s free Maximum Span Calculator for Wood Joists and Rafters, you should. Available in an online version and as a free download in the Android, iOS and Windows app stores, the calculator can be used to find code-permitted spans for all species and grades of commercially available softwood and hardwood lumber.
The AWC says that it has recently updated the apps to reflect the design values found in the 2018 National Design Specification (NDS) for Wood Construction Supplement (an update to the web-based calculator is scheduled for later this year). If you build decks, there’s an optional adjustment for wet service conditions, so that you can determine the allowable spans for PT southern yellow pine or incised Doug fir deck joists too.