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Mionnet's scale

A scale, 19ᵗʰ century, used to describe the size of coins, medallions, and similar flat round objects, published as an illustration by the French numismatist T. E. Mionnet in 1805.

The intervals are irregular and it is not known why Mionnet chose them. Since the scale was defined by a printed image, not numerically, and paper changes size at different humidities, it is not possible to say very precisely what Mionnet originally intended.

A number of authors republished the scale in the nineteenth century, but with varying dimensions.

Earle Caley measured specimens of these illustrations to an accuracy of 0.1 mm, and the figures in the table below are his. He cautions that, for the reasons mentioned above, a description of a coin's size given in Mionnet's scale are no more than 0.5 mm accurate, and probably less. See Caley's book for a full discussion of the scale.

The dimensions in the table below are diameters expressed in millimeters.

Scale Number	Mionnet, 1805	Leake, 1854		Dickeson, 1859	Prime, 1861	Head, 1887
1	8.9	I	9.3	9.5	7.5	9.3
2	12.1	II	12.1	12.5	14.0	12.3
3	15.4	III	15.3	15.3	20.1	15.3
4	18.1	IV	18.1	18.3	24.2	17.8
5	21.2	V	21.2	21.3	28.2	21.0
6	23.7	VI	23.8	24.2	32.1	23.9
7	26.6	VII	26.6	26.6	40.4	26.1
8	28.9	VIII	28.8	28.9	43.0	28.4
9	31.8	IX	31.4	31.3	45.7	31.2
10	35.2	X	34.9	33.9	48.3	34.7
11	37.7	XI	37.5	36.5	52.3	37.5
12	40.5	XII	39.7	39.0	55.1	39.7
13	43.4			42.1	57.8	43.2
14	51.8			50.4	60.3	51.0
15	56.7			54.9	62.9	55.9
16	60.6			58.7	65.8	60.1
17	64.5			62.8	68.6	63.2
18	70.9			68.8	71.6	69.8
19	78.3			75.9	74.6	77.0
20				83.1	82.1

T.E. Mionnet.
Description de Medailles Antiques.
Paris, 1805.

Page xiii and plate.

Earle R. Calley
Metrological Tables.
New York: The American Numismatic Society, 1965.
Numismatic Notes and Monographs No. 154.

See the Introduction.