How to know the rank of your keyword?

if you have for example website about weight loss ,and want to know the rank of keyword "how to lose weight ", this key word my rank number 1 at google or 100, how to know the rank of this keyword
i searched over the web and i find software called ranktracker ,download the program and install ,write your url or the competitor url and place the keyword you want to know ,this very important to know the progress of your website

See original post by sherio88