As I understand, cooking rice usually has a constant amount of water lost to steam. You need to have a rough idea of how much water your rice actually needs to absorb and how much is lost to steam. In my experience with my setup, rice usually requires an equal volume of water and 1 lost 1 cup of water to steam. So 1 cup of water requires 2 cups of water, 2 cups of rice requires 3 cups of water, etc.
So y = x + 1 where y is the cups of water and x is the cups of rice. 1 is the number of cups lost as steam.
Each time you open the lid you lose steam, so you may have to take that into account. I use a rice cooker and don't open the lid so I don't worry about that though.
Water lost to steam heavily depends on style of cooking, or more precisely, in a covered pot, is mostly a linear function of the excess heat beyond that required to bring contents to boiling temperature (steam re-condensation on the lid/sides provides a slight buffer) + a bit lost to empty space in the pot (when opening etc).
Some stoves are hard to regulate so the food is just barely boiling, so it can be hard not to notably lose water.
From experience, the boiling of water in itself is mostly meaningless when cooking, unless you want food extra shredded. You can happily cook at 90℃ or 80℃ if you want, but it will take longer.
Note if cooking risky food: beware of required time at a given temperature to kill pathogens, not forgetting heat transfer takes time especially in solid chunks.
In general, a rice cooker is indispensable and costs about $30. Plus you can walk away from it as it cooks, and you can put things on top of the rice to steam in there as well. (It will impart flavor though, so maybe don’t put greens in there unless you want broccoli-water flavored rice.)
So y = x + 1 where y is the cups of water and x is the cups of rice. 1 is the number of cups lost as steam.
Each time you open the lid you lose steam, so you may have to take that into account. I use a rice cooker and don't open the lid so I don't worry about that though.