Resolved Size of Backup external drives

I need to back up my Windows 7 computer. For the data, I just copy and then paste into an external drive. I recently read that I should do an Image Backup and in researching I found a site (Bob Rankin) that suggested Macrium Reflect. Well, I really know nothing about how to do this, but know I have to try and so I would like to know what size of external drive do I need to do this backup?

Thank you.

 

I might be best to just browse through this to answer any questions you might have.

 

Hi Bulldogs Sweety, Bill's link to Macrium looks really hard work so have a look at this link. It seems to explain what your question was about. The 6 Best External Hard Drives
What You Need to Know Before Buying an External Hard Drive