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Biblical and rabbinic length units, computed according to the halachic opinion you select. Part of the Ancient Measures collection.
Pick a halachic opinion, and every unit derives from its etzba (thumb-breadth): tefach = 4 etzbaot, amah = 24 etzbaot, mil = 2000 amot, parsah = 4 mil. The three opinions: Chazon Ish — etzba 2.4 cm, amah 57.6 cm; R. Chaim Naeh — etzba 2.0 cm, amah 48 cm; Rambam (Benish’s reading) — etzba ~1.9 cm, amah ~45.8 cm. Worked example (Chazon Ish): Goliath’s “six cubits and a span” (1 Sam 17:4) = 6 × 57.6 + 28.8 = 374.4 cm ≈ 3.74 m; by R. Chaim Naeh the same verse gives 312 cm. The opinions differ because the etzba is defined by a real thumb’s width — and thumbs differ. The article explains why.
The etzba is defined as a thumb’s width — and real thumbs differ. R. Chaim Naeh measured about 2.0 cm, the Chazon Ish about 2.4 cm. Archaeology (cubit rods, Gudea’s 49.5 cm Babylonian cubit) lands between them, and texts like Ezekiel’s ‘cubit plus a handbreadth’ show the standard itself shifted over time.
Rav Moshe Feinstein generally followed the larger, Chazon-Ish-like shiurim where stringency was at stake (lechumra) — for example for the minimum measures of matzah and maror — while often relying on the smaller measures to rule leniently (lekula).
Rabbi Chaim Benish’s study of the Rambam (Midos V’Shiurei Torah) derives an etzba of 1.90–1.92 cm — very close to the archaeological estimates and the common 45.7 cm cubit. This converter uses 1.91 cm.
2000 amot — but its length follows your chosen opinion: 1152 m (Chazon Ish), 960 m (R. Chaim Naeh), or about 917 m (Rambam). It is the Shabbat boundary distance (techum Shabbat).
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