How many bags would I need for a 16' x 5' x 4"

A 60 lb bag of QUIKRETE® Fast Setting Concrete Mix yields 0.45 cubic feet when placed. A 16 ft x 5 ft x 1/3 ft (4 inches) slab will require 26-2/3 cubic feet of concrete, or 45 bags (of 60 lb each) of QUIKRETE® Fast Setting Concrete Mix. QUIKRETE® Fast Setting Concrete Mix sets up in 20 to 40 minutes in 70 °F temperatures – more quickly if warmer, more slowly if cooler. Because of the fast setting time, it is important that there is sufficient equipment and labor to either allow you to pour the entire application before any of the material has set. If some of the material sets before subsequent bags are poured, a cold joint will form. A cold joint is caused by the inability of the product to intermix between bags, and prevents the application from being a single, solid mass. A cold joint may cause problems ranging from a simple aesthetic issue, to as serious as potentially allowing for water intrusion into the cold joint, which may eventually lead to concrete degradation. If a regular setting concrete is preferred, you may consider QUIKRETE® Concrete Mix (No. 1101), Pro Finish QUIKRETE® Crack Resistant Concrete Mix (No. 1006-68), or Pro Finish QUIKRETE® 5000 Concrete Mix (No. 100785). An 80 lb bag of any one of these concretes yields 0.6 cubic feet of concrete when placed, so 34 bags (of 80 lb each) would be required for 26-2/3 cubic feet of concrete. Yields will vary based upon waste, uneven subgrade, etc.

You will need 60 bags.