How many bags of Quikrete do I need for a 10 by 10 foot area at 2in thick

QUIKRETE® does not recommend placing concrete slabs at a 2” thickness, as they generally are too brittle for impact resistance. Typical slab placements (done with standard lumber) are 3-1/2” thick. At this thickness, a 10 x 10 foot slab will require 78 bags of 50-pounds each. Since this product sets in 20-40 minutes, we would recommend using instead QUIKRETE® 5000 High Early Strength concrete mix (#1007) or QUIKRETE® Crack Resistant Concrete Mix (#1006) as these are both normal-setting products. A slab of your dimensions will require 49 bags (of 80-pounds each) of either of these products. Yields will vary with waste, uneven subgrade, etc.