A typical paella uses about three volumes of water or stock for every one volume of rice. The commonly cited 3:1 ratio is higher than the ratio used for many covered rice dishes because paella cooks in a wide, open pan, where substantial liquid evaporates during cooking.
The liquid is usually added before the rice, often after meat, vegetables, or seafood have flavored the pan. It may be simmered first to develop a broth, and the rice is then spread across the pan. Once the rice goes in, traditional cooks generally avoid stirring it, helping preserve the distinct grains and encouraging a crisp socarrat layer at the bottom.
The 3:1 figure is a useful rule rather than an unbreakable formula. Rice varieties differ: bomba rice can absorb roughly two to three times its volume in liquid, while other varieties may require less. Pan width, heat, evaporation, and whether the liquid has already reduced also change the amount needed. Even so, 3:1 is the standard answer for a typical paella recipe.