On average, the typical A5 sized notebook (Leuchtturm, Hobonichi, Stalogy, Moleskine, Midori, Clairefontaine, Apica, Kleid, etc. ranging from 192 to 368 pages) has an equivalent square footage of writing surface to the front (only) of about 420 4 x 6 inch index cards. On a cost basis, for the same amount of money, on average one can buy 1,200 index cards for what they’re shelling out for equivalent notebooks.