Sizing up Shiurim: Modern-Day Measuring—Up or Down?
To calculate shiurim (halachic measurements), there are units used for linear measurement: etzbah (finger, usually calculated as the width of the thumb) or agudal (thumb-width), tefach (hand-breadth), amah (arm-length), among others. There are also units for measuring volume, such as: kezayis (like an olive), k’beiah (like an egg) and revi’is (a quarter [of a lug]). These measurements follow the sizes of average limb length and kitchen staples in ancient times.
What a Shiur Shares with Another
These shiurim work hand in hand. Each progressively larger shiur within a category is composed of multiple smaller shiurim: a tefach measures four agudlim and an amah is six tefachim. There are similar associations within the volume-based shiurim.*
Additionally, shiurim for volume are determined by length, width and height, so the size (or the capacity of a vessel) for a mitzvah item is gauged by both linear and quantitative measure. For example, the volume of wine required for Kiddush is a revi’is (which is also 1.5 k’beiah). A revi’is is detailed by Chazal via its dimensions—a sum reached by calculating 2 by 2 by 2.7 etzba’os, totaling 10.8 etzba’os.
The Shrinking Egg Phenomenon
However, over the thousands of years these measurements have been utilized, a growing discrepancy has been discovered in the relationship of these two categories, and noted by poskim across the ages: when calculating based on limb length, modern-day olives and eggs come up short. (In the above example of revi’is, the capacity of a cup with its dimensions totaling 10.8 average, present-day thumb-widths is much greater than the volume of 1.5 present-day eggs!)
The Noda B’Yehudah (18th century posek) writes in his commentary on the Talmud, Tz’lach, that this is on account of eggs having shrunk in size over the generations. To account for this change, he suggests that all shiurim that are based on volume should be multiplied accordingly. The current higher-volume shiur, popularly referred to as “the Chazon Ish shiur” is sourced in the original calculation of the Noda B’Yehudah and translated into modern-day measurements by the early 20th century authority of that name. According to the Chazon Ish, a revi’is is 149.3 milliliters (ml).
A (Small) Thumb in the Pie
Another contemporary posek, Rav Chaim Na’eh (early 20th century), extensively researched the matter, and among other calculations, based his measurements on the weight of a certain dirham (mid-Eastern coin)—a tradition going back in time to the Rambam (12th century early halachic authority). He reached an opposite conclusion: we should downsize our shiurim based on the current physical reality. Rav Chaim Na’eh’s revi’is measures 86.4 ml. At that time in Yerushalayim (where Rav Chaim was rav), this shiur was universally accepted. Today it is the common shiur in most of the world, and the Chazon Ish shiur is categorized as an extra chumrah (stringency).
(According to his calculations the shiur for agudal—which uses the modern-day amah as the base unit—is two centimeters, a measurement narrower than the width of the average thumb; this interpretation is made possible by using a modified definition of “average” and alternative techniques in measuring the thumb’s width.)
A Division and a Discovery
Some poskim maintain that we should disassociate the two types of measurements according to the current reality, and therefore measure length greater and volume in a lesser amount. This was the custom in many pre-war European communities. (Several theories have been proposed to justify this approach, but they are beyond the scope of this article.)
Some contemporary authors quote an even smaller shiur than transcribed by Rav Chaim Na’eh (e.g., 75 ml for a revi’is). This amount is sourced in Rishonim (the early halachic authorities), and correlates with the recent discovery of several old-time dirhams—curated Rambam-era artifacts unaccounted for by Rav Chaim Na’eh. One suggested rationalization to the disparity between this interpretation of a smaller agudal (approximately 1.9 centimeters) compared to the current average thumb width is that the measurement should be taken not on the face of the thumb but in its depth.
*Poskim argue about the correlation between kezayis to k’beiah. For more details on kezayis, see Halachah #235 and Halachah #537.
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