This question is a little broad for a couple of reasons.

1. The wealth of kings or nobles was highly variable depending on location and time.
2. The wealth of most nobles was tied to land ownership. The amount of actual liquid capital in a noble's fortune might be quite low.

A more readily answered question might be "how much land did a man have to own to be considered a noble in X time period and Y location? Alternately, if you're strictly interested in liquid capital (gold and precious materials) you might ask "How much gold could a well to do noble in X time and Y place pull together on short notice?"

If you want to know about multiple places I encourage you to break your question into several more specific questions and ask each of them.

/u/Vampire_Seraphin provides excellent suggestions. Also, keep in mind that the amount of gold today is extremely limited and before 1492, the holdings of the Old World was even less - in fact less than 1/10th of today's gold reserves. Since gold is really heavy, we're not talking about that much metal. See this source, for example. Silver was also a currency of wealth: Richard I was ransomed for 150,000 marks (65,000 pounds) of silver. This was an extraordinary amount, and it had to be raised (that is, it wasn't in the vaults available for this sort of event).