I need to convert 13.78 tons of bank sand to cubic yards? What is the formula?

Thanks

Not sure there is such a formula. Weight and volume are two different things. It would be like what's the formula to convert gallons to inches. However, I think folks who deal with hauling materials have a general idea of how large a ton of sand is. Wish I could help you further.

http://www.age.psu.edu/extension/factsheets/h/H20.pdf
Says bank sand is 2500#/cubic yard

So 13.78 tonnes is ~11 yards