Rice absorbs water at a 1:1 ratio. We typically cook 1 cup of rice using 1½ cups of water. (Or maybe 1¼; whatever.)

A ratio should scale, no? However, when cooking 3 cups of rice with 4½ cups of water, it's soggy and better suited to pudding by the end.

Was gibt ?

The rice cooking ratio does not scale because the extra ½ cup of water for 1 cup of rice represents not water to be absorbed, but the amount that's going to be released (think of it as "wasted") as vapor during the cooking process. Guess what? This amount released (because not really anything to do with the rice itself) will be the same for no matter how much is being cooked, but it does not add up to ½ cup water per cup of rice.

The temperature of the whole will rise to 212° Fahrenheit (100° Celsius) as it cooks. A rice cooker cleverly senses when the whole reaches that temperature and begins to rise above it. The cooker immediately turns off (begins the "keep warm" phase). That's what a rice cooker does for you and it mitigates the how much rice to how much water with quantity marks you must follow in the cooking pot.

A rice cooker is convenient, but unnecessary. All you need is a pot and a lid. Turn your finger into a rice cooker. Use the "first knuckle" technique.¹ (All my Asian friends have told me about this.) It works this way:

1. Wash, drain and add rice to the pot in the desired amount.
2. Add 1 cup of water for every cup of rice you started with.
3. Add enough more water to raise the level to the length of your finger from the end of your index to its first knuckle.
4. Adjust by experience for the length of your own finger(s).²
5. Get a tattoo around the first joint of the finger as a reminder. 😉 😂

¹ The last phalanx trick is to measure from the top of the rice (and not the bottom of the pan) up to the top of the water.

² Your fingers probably aren't so different that you really need to experiment. The index will do.

Thank our friend, Dan Souza, see The Best Way to Cook Rice ... and Ratios.