It doesnt work that way. Watts represent the power output of the amplifer. Decibels, or db, are a function of the output volume. This is a function of the impedence of the speaker (ohms) and how efficiently it transfers the output power into sound from the speakers. A simplified example is that a four ohm speaker will deliver about half as much volume as and 8 ohm speaker given the same power. Db level is characterized by this volume.
So, to answer your question, it cant be answered without more information. Be careful. When you start getting over 90 db or so, you star risking your ears. Oh, and the closer you are to the speaker, the higher db level. This is pressure on your eardrums and it can be very harmful in the long run. Not to mention, speakers sound better when you are not right up close to them. The room plays a big part in the sound quality.