The question was "How much wax does one use to wax a ski?"
Obviously there are many variables. Ski length and width just a part.
The type of waxes and prior base preparation all come into play here.
Here we use basic hydrocarbon waxes that are what is used for base preparation and "general" skiing. Then we talk a bit about high performance waxing. Unless you are super into it and racing etc. , don't worry about those fancy waxes. Main thing is wax with hydrocarbons well. Wax often. Scrape and brush well and fun you will have. This also assumes you have a well tuned ski.
Here we go!