It depends on the hub. 50 words per Amazon Capsule. It is recommended to use one capsule per text capsule. Once done, take a look and take in consideration as to whether or not the hub looks junkie. Then either remove some capsules or maybe one that you don;t want to get rid of, use the double arrow under the text box it would normally go with.
There is a box, at top right, when in edit mode that provides suggestions, etc about your hub.