One must be careful with all of the measurements that the Sages have measured out, for example kezayis (a measure the size of an olive) of Matza and a kezayis of Maror on the night of Pesach, drinking the four cups of wine, and the cup of Kiddush, and the cup of Grace after Meals, and the cup of Havdala, and the like, one needs to drink a Reviyis (a measurement of liquid), and it is not sufficient (to drink) less than a reviyis because then one enters into questions about the blessing afterwards for there are those who say that one needs to recite an after blessing on a kezayis and there are those who say one needs a reviyis. Therefore, in order to get out of questions in a case where one has to recite an after blessing, one must drink a full reviyis.
These measures apply to both men and women. There are those who make a mistake in this area and are not particular about measurements and their evil is great for if one is not particular to eat a kezayis of matza and a kezayis of maror, one finds that their blessing which they recited “upon the eating of matza” and “upon the eating of maror” is null and they are nulling a Torah commandment. Similarly, if one is not particular to drink four cups of wine (on Pesach), and kiddush and havdala and (to drink a cup of wine when reciting) grace after meals, one is not fulfilling the commandment and one finds oneself eating without kiddush and without havdala. If one then recites the after blessing, it is a null blessing for it too needs a measure.