When making espresso, there are so many variables to consider. All sorts of factors can impact your results including your water, grind texture, temperature, bean quality, and of course your measurements. Generally speaking, your standard double shot of espresso will be made with 17-18 grams of coffee. Of course, this may be adjusted depending on other variables and also to your personal taste. While you can use your portafilter to measure, it is best to use a kitchen scale for the best accuracy.
Another important measurement that will affect our espresso is brew pressure. In this instance, pressure is measured in bars with one bar equalling about 14.5 pounds per square inch, which is the level of atmospheric pressure at sea level. Optimally we will want our espresso to brew at 8-9 bars of pressure per square inch. If your espresso machine does not include a bar pressure gauge, you can also use extraction time to determine if you are within the correct brewing pressure range. Simply keep track of the time it takes for your machine to produce 2 ounces or 16 milliliters of espresso. Ideally, you will want to achieve an extraction time between 20-30 seconds.
Now, this is where grind size comes into play. Grind size will affect your extraction time and adjustments may need to be made to get within the proper range. If you are getting your espresso in under 20 seconds, you will want to adjust to a finer grind. On the other hand, if your espresso is taking longer than 30 seconds to extract, you will want a coarser grind. Importantly, you will want to keep your coffee dosing consistent throughout this process. In general, consistency between ingredients is extremely important for achieving a great espresso. If you are altering one measurement, keep in mind that you may need to alter others as well.