I approach this recipe, a ratio of 1:1:1.5, one cup of rice: one cup of beans: one and a half cups of liquid.  Regularly, I am only cooking this recipe for my husband and me.  So the most I would make is 2 cups of rice to 1 to 2 cups of beans.  The amount of beans depends if I am using my beans I rehydrated or canned beans.  If I use canned beans, I use the entire can, anywhere between 12-16 ounces (1.5-2 cups). If I use my beans, I might only use one cup of beans, as well as one cup of rice.  So I guess it boils down to what type of beans you will use—canned or rehydrated?

1. Rinse the rice until the water comes out clean and set aside. Measure one and a half cups of water also set aside and the cup of beans. Here is a great way to introduce flavor, swap the water for vegetable (or chicken, beef, or mushroom) broth. 
2. Dice about a cup of onions. Next, mince four cloves of garlic. Finally, add the garlic to the onions.
3. Heat 1 tablespoon of olive oil in a 6-quart kettle. Once hot but not smoking, add the onions and the garlic. Sautee the vegetables until translucent and soft.
4. Add the rice and quickly toss it around with the onions and garlic. We want to cover the grains of rice with oil. Add one to two tablespoons of achiote oil. If achiote oil is not available, add one tablespoon of olive oil and a teaspoon of turmeric, paprika, and/or a few sprigs of saffron. Tumeric will give you bright yellow rice. Paprika has a soft orange color. 
5. Add beans and toss in with the rice for a bit, then add your liquid. Allow the fluid to boil for about five minutes, uncovered. Do not stir. After five minutes of boiling and most of the liquid has evaporated, cover and reduce heat to the lowest setting. Let cook for another 15 minutes.
6. There should be no trace of water after 15 minutes. Then, with a fork, fluff the rice and remove it from the heat.