How many 80lbs bags do you need for a 16x14x2 slab?

A two-inch slab is fundamentally unsound because it's not thick enough. So...go with at least a three inch slab.

For a 16-foot x 14-foot x 3-inch slab:

The slab is 224 square feet.

Divide by four and you get 56 cubic feet.

Add 10 percent (because the bottom isn't flat) and you come up with 61.6 cubic feet.

There are 0.6 cubic feet in an 80-pound bag, so you need 103 bags.

Do not do it this way. It will cost you more money and the pour will be weak and look terrible. You need 2-1/2 yards of concrete from a concrete company. If you make the slab 4 inches thick, you will need 3 yards and that's better because concrete companies don't like to deal in half-yard increments.