OK, across the top it measures just shy of 2 inches by 1 1/2 inches. Height is 1 1/4 inches.
Here are the specs from the pump label:
Of course, this is Greek to me. I think the bigger issue would be that replacement pumps also have a wire out of the back of them which create the connection to the arm from the base which actually cycles it. Here are the pictures of what the actual pump looks like:
Back View with the wire: