how far will a pen write
A better measure for a pen's ink economy- and this is what they use in product testing- is writing distance. A dry ink ballpoint pen typically writes in the kilometer range- it can draw a continuous line of about 1-3km. For example, Papermate has a economy disposable pen line called Kilometrico. Bic pens fall into this category. A roller ball pen has a typical writing distance about 5-10 times less than that. Typically, 400-700m. A fountain pen has even poorer ink economy. My best guess is in the 100m-200m range, based on how often I refill my fountain pen vs replacing a roller ball.