In general, you should start with a small amount of rosin and increase the amount as needed. One way to do this is to hold the bow in one hand and the rosin in the other. Then, gently rub the rosin onto the bow with the palm of your hand. You should continue rubbing the rosin onto the bow until you hear a slight scratching sound.
If you are playing in a humid climate or a warm environment, you may need to use less rosin, as the rosin will become more tacky. If you are playing in a dry climate or a cold environment, you may need to use more rosin, as the rosin will become less tacky.
The type of rosin you are using will also affect how much you need to use. Some rosins are more concentrated than others, so you will need to use less of them. The type of violin bow you are using will also affect how much rosin you need to use. Some bows are made of different materials than others, which will require different amounts of rosin.
Ultimately, the best way to determine how much rosin to use is to experiment and see what works for you. You should also ask your violin teacher or a local violin shop for advice on how much rosin to use.