How far away is the kuiper belt from earth?

Somewhere upwards of about 30AU from the Sun. It's important to note that the "Kuiper Belt" is a THEORETICAL area; because it is so far away (and the objects suspected to exist there are so small) very few "Kuiper Belt Objects" have actually been identified. We'll actually have to go out there and look for them.

This is similar to the "Oort Cloud"; we've never detected an object in the Oort Cloud. We know that there has to be some sort of region, quite distant from the Sun, that acts as a reservoir for comets, because no comet could survive even 100 million years of close approaches to the Sun. And since the Sun is 4.5 billion years old AND we keep detecting new comets, they clearly are coming from SOMEWHERE.