I'm not 100% sure on that model number, but my older one was a NW- 150 and it was rated for 150 gallons. Not sure if the number is still equal to the rating.
This is just my own totally unscientific
method that I am sure people will take issue with, but, I divide the amount of air per hour a skimmer pulls by about 2 or 3. So if it pulls about 200gph of air per hour it would be a 66-100g skimmer. There is a lot more to it than that, and there are a ton of exceptions to this "rule" but it's generally accurate. Just stay to the lower side to be safe.
Again there is nothing behind that except for my own personal observations/experience.