One of the easiest ways to find a stock's short interest ratio is by going to Yahoo Finance, looking up a ticker you're interested in, and then clicking the "Key Statistics" link in the left-hand column. You'll find the short ratio on the right hand side of the page.
In my view, anything above 7 is a red flag. At that level, you're starting to get to the point where short selling makes up a big position in this stock, and investors need to be focused on who's in control. Anything below that level typically means that shorting is limited to investors who are hedging or using non-directional strategies like a pairs trade. You can ignore them.
The other metric to watch is the the percentage of float short. This stat measures what percentage of a stock's trading shares are currently bet against the company (unlike the short interest ratio, which focuses on shorting as a ratio of daily trading volume and how long it would take shorts to cover their bets). Again, if a large chunk of shares are bet short, there's the potential that sellers are in control of the market.
For simplicity's sake, you can find the percentage of a company's stock that's short in the same spot on Yahoo Finance...
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