How do you compare vermiculite quantities in quarts to cubic feet. The same with compost--40# bag is how many cubic feet?
One cubic foot dry=25.7 Quarts. 40# is weight and would depend on how wet the compost. Find a bag the same size that has the cubic ft on it and take a wild guess. Buy a bag and measure how many gallons/quarts It contains. Use the above formula for conversion.