Rice warmers are designed to keep cooked rice warm and moist until it is ready to be served. They can be either electrically powered or simply have enough insulation to maintain internal temperature. The power type, as in whether it is powered or not, as well as the actual capacity of each warmer are key considerations. Restaurants that intend to store the cooked rice in an area where no electrical outlets are available opt for a non-powered unit. A drawback to these models is that, although they are insulated and retain heat and moisture, the rice will slowly cool, a few degrees every 15 minutes or so. If the rice will be left I the warmer for more than a couple of hours, you should consider on that plugs in because it will maintain a constant heat, rather than slowly cooling off.
Rice container capacities are measured in how many cups of rice they will hold. Estimate how much cooked rice you will be placing in the warmer. Remember that cooked rice is about twice the volume of uncooked or dry rice, so 25 cups of dry rice will equal around 50 cups of cooked.