Southern Pine and Decks.com offer tables for joists, rafters, headers and beams. The American Wood Council provides a maximum span calculator for wood joists and rafters.
The tables provided by Southern Pines were compiled by the Southern Forest Products Association and are accurate for normal loads under specified moisture levels. Ratings are also categorized by live load, dead load and joist type. Decks.com provides post spacing information based on joist length and the species of wood being used. The American Wood Council's calculator provides tables based on the species of wood, size of the joist, grade of the lumber and type of joist. The tables include maximum horizontal span, minimum bearing length, bending strength, shear strength and bearing strength.