how many photos can you store in cloud with 50 gb?

If each photo was 1 GB in size, 50 photos.

If each photo was 1 MB in size, 50000 photos

1GB = 1000MB

Sorry, but your question falls to the answer of "50 GB worth of photos." As dialabrain has mentioned, the actual number of photos will depend on the size of each photo. This is no different than any other type of file and its storage requirements.

What I suggest that you try is to find out how large your Photos Library is to get an idea of, whether or not, 50 GB is large enough to store it. One method to do that is select the Photos Library, located at ~/Pictures/Photos Library. Then right-click on Photos Library, and then, select Get info from the pop-up menu.

Just to add, if you had 60MB RAW photos it you could save 833 photos. If you have 1MB JPEGS, approx 50,000. So it varies.

Just to add to Bob's comment. If you had a 50 GB photo, one.

That would depend on the size of each photo and what format they are. Lots.