How much will I need to make a 2 - 24 in x 12 in concrete forms for lawn decorations?

A 60 lb bag of QUIKRETE® Fast Setting Concrete Mix yields 0.45 cubic feet when placed. The number of bags required will depend upon the thickness of the forms. If the forms are 3.5 inches (0.29 ft) thick, two forms each of dimensions 2 ft (24 inch) by 1 ft (12 inch) by 0.29 ft (3.5 inch) form for lawn decorations will require 1.2 cubic feet of concrete, or 3 bags (of 60 lb each) of QUIKRETE® Fast Setting Concrete Mix. Yields will vary based upon waste, uneven subgrade, etc.