That all depends on your envirnoment around you. Do you live in a high humidity environment or a desert environment? It all depends on the air around you and whether the air will help with the water dissapating or not. High humid environments you will water less.
naw, dont worry about measurements, Just water it when it needs it. NOTE that wen the plants are small And there isnt alot of roots compared to the bucket size, make sure u only water it a little bit. As the plant gets bigger, u will need to water more area.