How many pictures can a 16GB memory card hold at 12 megapixels?

You can put about 2300+ 12 pixel JPG pictures on an 8 gigabyte SD memory card. But, JPG images vary a lot in size on disk, so there's no way to know exactly, it depends on what you are taking pictures of. You can get many more than 2300 pictures of a plane white wall. An many less pictures of a basket of multi color variegated marbles. Also, an 8GB memory card only has room for a little less that 7 1/2 GB of storage.