Marginal utility is the additional utility derived from the consumption of one more unit of the given commodity. It is the addition made to the total utility by consuming one more unit of any product. It the change in total utility divided by the change in the number of units. For example, if one is thirsty, he drinks one glass of water he gets some satisfaction. If he drinks a second glass of water he gets a certain level of satisfaction. Now the difference between the level of satisfaction by drinking from both the glasses is MU.