Not sure on which forum to post this, but this is something that's been puzzling me for a while now. I learned to drink and appreciate espresso when I lived in Italy for a while. When I bought my first espresso machine later, I was taught that according to official Italian standards set by the National Institute for Espresso (in Italy) one cup of espresso requires approximately 7 grams of ground coffee and should produce about 25milliliter of espresso. A while ago I upgraded to an E61 HX machine (Bezzera Magica) and got into reading forums like this one and watching youtube video's to improve my skills. I noticed that people seem to accept a brew ratio of approximately 1:2 or 1:2,5 max as a standard for espresso, at higher ratios they will say it's a lungo. Going back to the official Italian recipe for espresso, although obviously 25ml's isn't exactly 25 grams, I would still assume this corresponds more to a brew ratio in the range of 1:3 - 1:4. How does this add up, if it adds up at all?

25 mL (with Italian-style crema) is not 25 g

The "official" marketing standard is weight to volume. Most people talk weight to weight.

Edit: 7 g shots with most current home machines is very challenging without a special basket and tamper. See, for example 7 gram single shot?? Mission impossible!

Does it really make that much of a difference, like would 25 ml's be 14 grams making it a 1:2 ratio? Seemed hard to imagine to me, but maybe you're right..

14g is about right for 25ml given traditional Italian blends and roast levels.