Plate Dimensions

Several of those who saw and handled the metal plates of the Book of Mormon provided detailed descriptions of their dimensions. Numerous sources give approximate measurements of the length and width of the plates in inches, such as Joseph Smith’s statement in the Wentworth letter that “each plate was six inches wide and eight inches long.”¹ Other sources give these same dimensions, while yet others give minor variations, describing the plates as slightly smaller (about six by seven inches) or slightly larger (about seven by eight inches).² The thickness of the bound stack of plates was also consistently estimated as being between four to six inches in height.³

The approximate thickness of each individual plate is harder to determine. An early newspaper report states that the plates were an eighth (0.125) of an inch thick,⁴ but witnesses usually did not give a measurement, but rather described them in reference to other thin materials.

Joseph Smith, for instance, said they were “not quite so thick as common tin.”⁵ Each of the three witnesses—Oliver Cowdery, Martin Harris, and David Whitmer—were also reported as describing the individual plates as being similar to the thickness of tin plates.⁶ Other reports make comparisons to the thickness of window glass.⁷ Joseph Smith’s wife, Emma, remembered moving the covered plates around while cleaning, and said that they “seemed to be pliable like thick paper, and would rustle with a metalic sound when the edges were moved by the thumb, as one does sometimes thumb the edges of a book.”⁸

Estimating the Thickness of the Plates

In recent years, researchers have attempted to more precisely estimate the thickness of each plate, based on these descriptions. One method is to determine the thickness of the items they were compared to. For instance, some sources describe them as being the thickness of window glass, which measured between 0.055 and 0.061 inches (about 0.14 and 0.16 cm) in that time period.⁹ Witnesses more often used common tin as a reference point when describing how thick the individual plates were. However, the exact thickness of tinplate in the nineteenth century could vary widely.¹⁰ Based on various sources and measurements, Bruce Dale determined that the average thickness of tinplate was approximately 0.016 inches (about 0.04 cm).¹¹

Another method is to determine how thin the plates would need to be in order to be “pliable” and make a metallic rustling sound when their edges were thumbed, as Emma described. According to several studies, the plates were likely made of tumbaga—an alloy of copper, gold, and sometimes silver—with a high copper content.¹² Working off this assumption, Jerry Grover conducted experiments to determine how thin copper sheets would have to be in order to be flexible enough to make the reported rustling sound.

He was able to produce “the rustling type sounds described by Emma Smith” when testing copper sheets between 0.004 and 0.01 inches (about 0.01 to 0.025 cm).¹³ When repeating the experiment with sheets made of a tumbaga-like alloy made of copper, gold, and silver, he determined that these would need to be close to 0.007 inches (about 0.018 cm) or thinner in order to produce the desired rustling sound.¹⁴

Since witnesses described the Book of Mormon plates as being engraved on both sides,¹⁵ Grover also conducted tests that confirmed soft copper sheets as thin as 0.005 inches (about 0.013 cm) could be successfully engraved on both sides without the engravings pushing through. “Therefore alloys [like tumbaga] that are harder than soft copper at this thickness can be satisfactorily engraved [on both sides].”¹⁶

Although these comparisons yield varying results, all of them suggest that the plates were very thin, ranging between a sixteenth of an inch on the upper end to less than a hundredth of an inch on the bottom end.  

Ancient Inscribed Plates with Similar Dimensions

A set of nineteen gold plates, bound together by hinges, was discovered in South Korea and dated to between the sixth and seventh centuries AD.¹⁷ Although they were engraved in a manner that only allowed them to be written on a single side,¹⁸ these Korean plates appear in other respects to be very similar to those of the Book of Mormon.

Each plate is 17.4 x 14.8 cm (about seven by six inches) and a only 0.15 cm (about 0.06 inches) thick—similar to the thickness of window glass in the nineteenth century.¹⁹ Furthermore, one can visually see various bends and creases in the plates in high resolution images, making it easy to imagine the rustling sounds they might make if moved and unfolded. Minor signs of wear and tear notwithstanding, they appear to be remarkably durable, having likely been opened and used for study many times over the course of decades and yet remaining in surprisingly good condition.²⁰

Other plates with similar dimensions to the Book of Mormon have been found with inscriptions on both sides. For example, numerous copper or bronze plates measuring 21 x 18 cm (about eight by seven inches), have been found in Japan. Some of these are reported to be as thin as 0.2 cm (about 0.08 inches) and were written on both sides.²¹

Thin Pre-Columbian Tumbaga Sheets

Although inscribed metal plates of similar dimensions have not yet been reported in the ancient Americas,²² there is evidence that skilled ancient American metalworkers knew how to make thin sheets of tumbaga within the specifications described for the Book of Mormon plates. For example, a small tumbaga artifact was recovered in Belize which likely dates to “somewhat before AD 500” based on its archaeological context.²³ The object was made from “thin sheeting, which was probably hammered and annealed …. Thickness of the sheeting is about 0.03 to 0.04 cm [about 0.012 to 0.016 in].”²⁴ This means that tumbaga sheets that could aptly be described as “not quite so thick as common tin” were available in Mesoamerica close to the time of Moroni.

Some skilled pre-Columbian metalworkers could produce even thinner tumbaga sheets with impressive consistency. Warwick Bray notes, “Analysis of archaeological specimens from the north coast of Peru shows that in this area the preferred alloy was a mixture of gold, silver and arsenical copper and that the resultant metal was worked by alternate hammering and annealing into sheet 0.2 mm [less than 0.008 inches] thick, the perfect evenness of which compares well with that of today’s machine-made product.”²⁵ Thus, ancient Purvian metalsmiths could create tumbaga sheeting within less than a thousandth of an inch of the thinness proven to have the pliability needed to “rustle with a metalic sound.”

Therefore, tumbaga plates consistent with the specifications described by the witnesses could have been made by ancient American metalworkers.

Conclusion

The dimensions of the individual plates, as described by the witnesses, have precedents in the ancient world. Inscribed gold plates could be made thin enough to make a metallic rustling sound, as described by Emma Smith, while maintaining their form and durability. Furthermore, ancient American metalsmiths were capable of working tumbaga into thin sheets consistent with the descriptions of the witnesses. Thus, the witnesses’ descriptions of the dimensions of the plates, and particularly the thinness of the individual plates, are consistent with the known skills and abilities of ancient metalworkers, both in the Americas and elsewhere. This supports the conclusion that they were describing a real ancient metal artifact that they had seen and/or handled.

Jerry Grover, Ziff, Magic Goggles, and Golden Plates: Etymology of Zyf and a Metallurgical Analysis of the Book of Mormon Plates (Provo, UT: Grover Publishing, 2015), 67–95.

Kirk Henrichsen, “How Witnesses Described the ‘Gold Plates’,” Journal of Book of Mormon Studies 10, no. 1 (2001): 16–21, 78.

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Testimony of the Three Witnesses

Testimony of the Eight Witnesses