is there a software out there that you can add your text and see what your keyword ratio is? what should your keyword ratio be?
There are many online tools. But I would recommend you to use Google Web Masters tools & Bing Web Masters Tools so that you can get more information about your site.
The most commonly accepted keyword ratio is 2-3% I think. I would concentrate on making the content interesting and engaging to users first and then integrating 3-5 keywords per page.
try seoquake addon for firefox, you can view features "keyword density" to analyse your text. for me keyword ratio maximum 10% minimum 2%
Keyword ratio is irrelevant unless you are using too many keywords. Just write in normal grammatically correct english and you will be fine.