There cannot be a defined capacity sufficient for all users as different people use the microwave ovens for different applications. To give you a better perspective, consider the general amount of food consumed in a large household compared to the food required in a small family. While a small capacity option is certainly unusable for a large family, you can simply get the highest capacity variant available under your budget, and rest assured that it can be sufficient for small applications as well as come in handy for possible large parties.