One cubic yard is equivalent to 27 cubic feet. The actual calculation is 3 feet (length) times 3 feet (width) times 3 feet (depth) (3x3x3) = 27 cubic feet (one cubic yard). Picture in your mind a square cube like a wood block or a Rubik's Cube. This will give you an idea of what a "cubic" yard is.
A standard bag of shavings is approximately 5.5 cubic feet (cf) and costs approx. $5.75 each. For 5.5cf bags, it would take approx. 4.9 bags of shavings to be equivalent to one cubic yard of bulk shavings at a cost of $23.75 per cubic yard (4.9 x $5.75). For 6.5cf bags, it would take approximately 4.2 bags of shavings at a cost of $24.15 per cubic yard (4.2 x $5.75). The cost difference is in the manufacturing. Since it costs extra money for the machines, labor and cost of the plastic to put the shavings into, all of the extra costs are being passed onto the consumer. All of this excess cost is eliminated by buying in bulk.
To figure out how much shavings you would need to fill each stall, the actual calculation would be:
length of stall, times width of stall, divided by:
75 for 4" deep
100 for 3" deep
150 for 2" deep
so a 12x12 stall calculates to 12 times 12:
divided by 75 for 4" deep = 1.92 cubic yards per stall
divided by 100 for 3" deep = 1.44 cubic yards per stall
divided by 150 for 2" deep = 0.96 cubic yards per stall
For 10 stalls, measured at 12x12 that you want bedded to 3" deep, the calculation would be 1.44x10=14.4 cubic yards.
I hope I was able to put this into simple terms that everyone can understand since it can be very confusing. If you need any further help on the conversion from cubic feet to cubic yards, I am always available to answer any questions.