https://ripple.com/faq/How many ripple credits (XRP) are there?
When Ripple started there were 100 billion ripple credits in existence. This number is slowly decreasing because, as a security measure, each transactions destroys a tiny fraction of a credit. Don’t worry — even with the whole world using Ripple, it will take thousands of years to destroy all the credits. You can see the exact number of credits at the Live Network Graph
Bitcoins 21 million limit
Litecoin 84 million limit
XRP 100 billion limit
You can see what there actual worth may be ?