Typically dry beans expand 2-3 times their original volume when soaked, depending on their age (fresher beans have more moisture left than older ones and expand less).
I usually put them in a large pot and cover them with at least 5-6cm of water above.
Here is an image of a dry pinto bean next to a pinto bean that I soaked for 8 hours. You can see that the soaked bean is about 3.5 times the size of the dry bean. 4 cups of dry beans will turn into ~12 cups of soaked beans.
I measured by volume, not weight. 3/4 cup of navy beans came out to just over 1 3/4 cups after cooking. After soaking them overnight, they were just about doubled. After cooking they were roughly 2.5 times the dried volume.