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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?
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They assume an average thickness of a matza. You can back calculate what that is – Double AA 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. – Shmuel Apr 30 '14 at 4:44
That could be about the thickness of regular matza, no? – Double AA 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. – Shmuel Apr 30 '14 at 5:28
Why would its being Shmura make a difference? – Double AA Apr 30 '14 at 5:31

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