UVW Unwrap scale to fit

[glorybound]

When I unwrap my UVW how do I scale it to fit in the box. I can manually scale it, but it isn't predictable, so can I scale to fit?

[lukx]

tools - pack uvs

[glorybound]

it takes all the pieces and randomly shoves it in the box. I tried to just scale it, but sometimes it works, and sometimes it doesn't. Sometimes it jumps so small I can't scale it back up and other times it will not scale at all.