For stocks there is the number of outstanding shares which, in conjunction with share price, shows the market cap of a stock (e.g. Stock XYZ has 1MM shares outstanding at $100 each, giving XYZ a $100MM market cap). Is there an equivalent view of shares outstanding for stock options? E.g. Company XYZ Call options of $110 Expiring on 12/7/18, there are 50k options outstanding (aka 50k of these options have been purchased).

I keep reading in various places that there is a lot of Short sell interest of stocks like Tesla, and various figures thrown around of how many $billions short sellers are set to lose if the stock price increases (aka doesn't drop to the put mark), but I haven't discovered what data is used to make these calculations.

Many thanks