Updated: Jul 30, 2020
Coffee bean is a natural product, it does not have a standard weight. Espresso shots on the other hand, are standardized by weight - 7 gm for a single shot and 14 gm for a double shot. From there, one could vary the dosage based on one’s taste preferences and size & type of espresso basket used.
On an average the weight of one coffee bean is around 0.15 gm; but it could be more for lighter roasts or less for really dark roasts. So 42 beans will give you approximately 6.3 gm, slightly under the 7 gm required to make a standard single shot of espresso.