In order to fulfill the mitzva of kiddush there must be enough wine in the cup to be considered significant, so that the berakha is recited over something. This amount is the volume of an egg and a half (one fourth [revi’it] of a log, commonly referred to simply as a revi’it), which is the minimum amount that must be present in any cup being used to fulfill a mitzva (kos shel berakha). If less than this amount is used, the mitzva has not been fulfilled (Shabbat 76b; Pesaĥim 107a, 108b; MA 271:32).
For many years it was assumed that the egg and a half that Rambam mentions was the equivalent of 86 ml, based on the opinion of R. Ĥayim Naeh. However, more precise calculations show that the amount is really 75 ml. Some are stringent and maintain that the eggs nowadays are only half the size that they once were, so that the amount of wine in the cup must be doubled to 150 ml. (Ĥazon Ish). In practice, the bottom line is that one may make kiddush over 75 ml of wine, but many Ashkenazim are stringent le-khatĥila to use 150 ml.
After making kiddush, one must drink a “melo lugmav” – the amount of wine that could fill the drinker’s cheek if he puffed it out – considered the smallest amount that has a relaxing effect on the drinker. This corresponds to the majority of a revi’it, or at least 38 ml, but one with a bigger mouth must drink more. For most people this amount will be between 50 and 55 ml, but nobody, even a giant, must drink more than a revi’it.
If the person making kiddush is unable to drink a melo lugmav, one of the listeners can do so instead. Be-di’avad, if a cheek full is drunk collectively, all have fulfilled their obligation, even though no individual drank a cheek full (Pesaĥim 107a; SA 271:14; MB ad loc. 73).
. See Peninei Halakha: Berakhot 10:11 or Harĥavot here. In brief, a mistake was made when R. Ĥayim Naeh calculated the amount according to Rambam. The measurement of a dirhem (drachma) in use in Rambam’s age was a bit smaller than the Turkish dirhem that R. Naeh used in his calculation. Accordingly, Rambam and those who follow him maintain that an egg and a half (which corresponds to a revi’it) is 75 ml. Thus writes R. Beinish (Midot Ve-shi’urei Torah 30:5; 16:6); R. Ovadia Yosef agrees. (Early Ashkenazic custom was to consider an egg’s bulk to be 46 ml and a revi’it to be 69.) However, Noda Bi-Yehuda states that eggs are only half the size they once were. Ĥazon Ish adopts this approach, calculating accordingly that an egg and a half is about 150 ml. MB states that when the mitzva concerned is rooted in the Torah, such as kiddush on Friday night, it is preferable to be stringent and follow Noda Bi-Yehuda. However for rabbinic mitzvot such as the four cups at the Seder and the requirement to make a berakha aĥarona, one need not follow the double shi’ur even le-khatĥila. This is also explained in Peninei Halakha: Pesaĥ 16:8; 16:23 and n. 20 ad loc.. If the person making kiddush drinks less than a melo lugmav, and everyone collectively drinks less than a melo lugmav, they have not fulfilled the mitzva as instituted. According to MA 271:32, they did not fulfill it at all, and the one who made kiddush must continue to drink until he reaches a cheek full. If he had already become distracted, he must make another berakha over the wine. If he got up and went somewhere else, he must make kiddush again. However, according to some poskim, even though he did not fulfill the mitzva of kiddush properly, he nevertheless fulfilled it be-di’avad, since he did make kiddush over a cup of wine. This is the opinion of Kaf Ha-ĥayim 271:82 and Or Le-Tziyon, 2:20:7. See SSK 48:9 and n. 57. Since one is in doubt about the law, one who did not drink a melo lugmav may not say kiddush again, but should try to hear kiddush recited by someone else.