Typically about 15 - 18 gm of coffee beans are needed per cup. The actual quantity will vary according to method and individual taste preferences. We grind coffee beans as per our needs and use it immediately.
Coffee brewing works on ratios.
To make a cup of french press style coffee, we use a coffee to water ratio of 1:13, i.e. 17 gm coffee in about 220 ml of hot water.
For drip & pour overs style coffee, we use a ratio of 1:15, i.e.15 gm of coffee and 225 ml of hot water.
While making espressos, we prefer a ratio of 1:2.5, so about 18 gm coffee to get a 45 ml shot and so on.