The amount of CC's (Cubic Centimeters) to HP (Horsepower) is not a completely standard rate because it all depends on the tuning of engines, however the rule of thumb is that there are 15-17cc's to 1 hp.
To answer your question, 16hp is around 250cc's (though this may range from around 240-272). To get the figure you multiply the 16 horsepower by either 15,16 or 17 and this will give you the number of cc's.
This is a very average estimate, although it really depends what kind of engine you are using. At that size it's unlikely to be an oil tanker or a fighter jet, but it's important to remember that this rule is really only suited to cars and motorcycles.
If you want a more accurate reading for a motorbike, this website is a good way of calculating the number of cc's: http://www.nightrider.com/biketech/calc_displacement.htm
Or if you are interested in more rate's for your engine, here is the relationship between cc's and ml (millilitres): //science.blurtit.com/1237885/60cc-equal-to-how-many-ml