The amount of coffee to put in a portafilter depends on a few factors: -Portafilter size - Smaller 49-53mm portafilters hold 14-18g of coffee, while larger 58mm ones hold 18-22g. -Type of roast - Lighter roasts are denser and require more coffee by weight. Darker roasts are less dense and use less. -Desired shot size - The more coffee in the portafilter, the larger the shot volume will be. Aim for around 2:1 ratio of dry coffee to espresso output. -Grind size - Finer grind means more coffee by volume fits into the portafilter basket. Coarser grind takes up more space. -Tamping pressure - Heavy tamping can compress more coffee into the basket. Light tamping fits less. A good starting point is: For a single shot - Use 14-18g of finely ground coffee in a 49-53mm portafilter. Can go up to 20g if using a 58mm. For a double shot - Use 16-20g in a 53mm basket or 18-22g in a 58mm. Don't overfill. Dose the portafilter, distribute evenly, then tamp evenly to compress the grounds. Dose can be adjusted based on shot time and taste. The key is being consistent with your dosing each time.