That would be gain ratio, which is obviously personal depending on your crank length and also your wheel size and tyre size. The gearing charts are a nice basic way to compare gears to gears. If you're picky, most of the available tables reflect a nominal 27" wheel rather than the now most widely used 700C wheel. Gain ratio only really matters if you're comparing one person's gears to another person's. If you're looking at your own, the other factors outside of chainring/cog cancel each other out