Sephardic Jews customarily do not give any consideration to the Noda Bi-Yehuda/Ḥazon Ish position, because their own tradition about these measurements was handed down in an orderly manner from generation to generation. Even with regard to Torah commandments, they are not concerned about the Ḥazon Ish shi’ur. It follows that the volume of a kezayit does not exceed one third of a piece of machine matza (based on the position of Tosafot that a kezayit is about half an egg).
The above applies when one measures by volume; however, the custom of many Sephardim is to measure the shi’ur by weight, as it is difficult to calculate the volume of each food independently to determine whether one must recite a berakha aḥarona after eating it. After all, foods come in all sorts of shapes and sizes: long and thin, round and square, etc. Some foods contain hollow spaces that are not factored into the volume. Thus, in order to make it easier to calculate shi’urim, the practice of measuring by water weight was adopted. It was thus determined that a kezayit, or half an egg, is equal to 29 grams (a more recent adjustment puts it at 25 grams). In order to eat this amount of matza, one must eat nearly a whole piece of machine matza. In other words, if we calculate a kezayit of matza by weight, it comes out almost three times more than if measured by volume.
Accordingly, one must eat four machine matzot on the Seder night: two after the initial berakhot, one for korekh, and one more for the afikomen. Many Sephardim do so (and some are stringent and eat two matzot for the afikoman).
Yet is it clear that in principle all measurements are by volume, not weight, as several leading Sephardic poskim – R. Ben-Zion Abba Shaul and R. Shalom Messas – have ruled. Since the stringency of measuring matza by weight raises justifiable difficulties and consternation among many participants, we may instruct all Jews, Sephardic and Ashkenazic alike, that a kezayit is a third of a machine matza.
Additionally, since our custom is to eat two kezayit-sized pieces initially, one must eat two thirds of a machine-made matza. Even according to the weight-based measurement, two thirds of a machine-made matza constitutes a kezayit according to Rambam.
It should be noted that according to the latest calculations of Rambam’s opinion, it emerges that the weight of half an egg is c. 25 grams, not 27, 28, or 29 grams as calculated by those who follow R. Ḥayim Naeh. See Peninei Halakha: Berakhot 10:6, 11. Nevertheless, the key point is that we calculate by volume, and by eating one third of a machine-made matza, one removes all doubt. See Sidur Pesaḥ Ke-hilkhato 2:8:4. Sephardim who eat thick, soft matza may also calculate by volume, since this is the primary halakhic method. However, it is easier to eat a weight-based (25 gm) kezayit of this matza. After the initial berakhot, when we eat two kezeytim, one may use Rambam’s kezayit, which is less than a third of an egg, and c. 30 gm of matza would suffice in this instance.