I've never measured, just use my hands.
Rice in, water until it almost covers your hand. Or, one knuckle of rice, one knuckle of water. Bring to a boil with the lid off, then cover and let sit.
The thing I've found is that every type of rice and each batch is a bit different. Some need less/more water than others...
Oh! The rice I bought last month had odd instructions. Boil a large quantity of water, then add the rice. Cook for (10?) minutes, then drain. Anyone tried that? Seems like you'd be making soup...
ETA: That seems like Britwife's recipe, too. I'll try it some time!