Rookie question--align sidebar length to content

Greetings, apologies in advance if this is obviously rookie. I have several pages where I want to display a right sidebar with several widgets (contact, images, etc.) I prefer to have the left content box the same length as the sidebar. Where the content itself doesn't naturally extend to the same point on the page as the fixed content in the sidebar, what options do I have to force the two to line up? Thanks in advance for recommendations.