Modii to US Gallons (modius to gal)

1 modius equals 2.307102591 US gallons (rounded).

1 modius = 2.307102591 US gallons

How to convert modii to US gallons

To convert modii to US gallons, multiply the number of modii by 2.307102591. The factor is rounded to 10 significant digits. To go the other way, multiply US gallons by 0.4334440974 (rounded).

US gallons = modii × 2.307102591

Example: 10 modii = 23.07102591 US gallons.

Pints, quarts, gallons and fluid ounces differ between the US and the UK. Units are labeled 'US' or 'imperial' to avoid confusion.

Approximate value. Standards for the modius varied by place and period, so this converter uses the most commonly cited value. Treat results as estimates, not exact figures.

About these units

Modius (modius)

Ancient RomanHistorical unit (no longer in standard use)Approximate value

Sixteen sextarii, about 8.73 L. The standard Roman dry measure, used for grain.

Grain, not wine, was what the modius measured. It belonged to the Roman dry scale, where it stood at the top of the ordinary series, with the semimodius at half its size and the larger modius castrensis, about 12.93 L, above it. Wikipedia's table gives the plain modius as 8.73 L, the figure used here, and describes it as 2 and two thirds congii or 16 sextarii.

That puts it at one third of an amphora quadrantal, so liquid and dry measures shared a single system built on the cubic Roman foot. Because it is a multiple of the sextarius, the usual uncertainty applies: surviving vessels suggest the sextarius ranged from 500 to 580 mL, which would put the modius between roughly 8.0 and 9.3 L. A bronze modius stamped with a reference to imperial regulation of weights and measures survives, which shows that the state tried to keep the size fixed. Today it is a little under a quarter of a US bushel.

1 modius = 8.733333333 liters (approximately).

Sources: Wikipedia: Ancient Roman units of measurement

US Gallon (gal)

US customaryCurrent unit

Exactly 231 cubic inches or 3.785411784 liters (128 US fluid ounces). About 17% smaller than the imperial gallon.

The US gallon is a survivor of English wine trade. Around 1706, a statute in Queen Anne's reign fixed the wine gallon at exactly 231 cubic inches, settling confusion among the competing gallons for wine, ale and corn. British colonies in North America used that wine gallon, and in 1824 Britain replaced all its gallons with a new imperial one while the United States kept the old measure. It was adopted as the legal US standard in 1836 and is still defined as exactly 231 cubic inches, or 3.785411784 liters.

That makes the US gallon about 17 percent smaller than the imperial gallon, a difference that explains why American and British fuel-economy figures cannot be compared directly. Everyday uses are milk jugs, paint cans and gasoline pumps. One gallon divides evenly into four quarts, eight pints, sixteen cups and 128 fluid ounces. A gallon of water weighs a little over 8 pounds, an easy figure to remember when loading a car with water jugs.

1 US gallon = 3.785411784 liters (exactly).

Sources: Wikipedia: Gallon; NIST SP 811, Appendix B.8: conversion factors for volume

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