# How much Matzo must one eat on Pesach?

According to the OU, one must eat a minimum of "approximately 26 cubic centimeters" of Matza and Marror to fulfill his requirement (ie, a kezayis is 26 cm3). They also provide a chart, which states that one must eat a piece of matzah that is "6.25 x 7 inches". Converting that to centimeters (1 in = 2.54 cm), we get "15.875 x 17.78 cm," for a total area of ~282 square centimeters. (This chart is also published by other organizations, for example here.)

• What is the source for the number "26 cubic centimeters?"

• Assuming that number is the total volume of a kezayit, how does the chart make any sense?

• How does one convert this 2-dimensional chart into a 3-dimensional piece of matzah?
• They assume an average thickness of a matza. You can back calculate what that is Apr 30 '14 at 4:32
• If I've done my math correctly, it works out to 0.09cm, or 0.9mm. Which is about the thickness of a mechanical pencil lead. Apr 30 '14 at 4:44
• That could be about the thickness of regular matza, no? Apr 30 '14 at 4:58
• Maybe. I no longer have any Shmura Matza left over to measure, but the machine matza is about 50% thicker. It's hard to measure this stuff, though. Apr 30 '14 at 5:28
• Don't know what's uniquely technical about using regular words with their standard accepted definitions. Apr 30 '14 at 20:37

• What is the source for the number "26 cubic centimeters?"

As Ikar Tosafot Yom Tov on the Mishnah in Peah.8.5 says (as per the Rambam):

קב. אודיעך בכאן שיעור כל מדה מהם ושמור אותה תמיד בכל המשנה. ובתחלה נאמר כי במדה שיש בחללה ד' אצבעות על ד' אצבעות ורומה ב' אצבעות ושבעת עשיריות מאצבע, ויהיה זה האצבע ששיערו בו מאצבעות היד הגודל. וזו המדה אשר יש בחללה זה השיעור שזכרנו בשום תבנית הוא נקרא לוג והרובע ממנו הוא נקרא רביעית. וחצי הרובע שמינית. ויש בקב ד' לוגין. הר''מ:‏

The Log is 4 x 4 x 2.7 Ezba. A Reb Chaim Noeh Ezba is 2 cm, giving us a Log of 345.6 cm3.

A Log is 4 Revi'is, a Revi'is is 3 Kezaizim - so a Log is 12 Kezaizim.

1/12 of 345.6 gives us 28.8 cm3 - so using this system it seems that - for some reason - the OU is using a slightly smaller shiur than the classic Reb Chaim Noeh Ezba shiur of 2 cm per Ezba.

• How does one convert this 2-dimensional chart into a 3-dimensional piece of matzah?

They are assuming some standard height of a Matzah - I guess they measured a lot of crushed Matza and got some average that they are comfortable in publishing.