A 2×12 (2-by-12) floor joists can span up to 23 feet 3 inches, 2×10 (2-by-10) up to 19 feet 1 inches, 2×8 (2-by-8) up to 15 feet & 2×6 (2-by-6) up to 11 feet 4 inches at 16″ spaced by using southern yellow pine graded as #1 when live load of 30 lbs/ft^2 & dead load of 10 lbs/ ft^2. How much does a cubic foot of gravel weigh.