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Thickness.  The measurement of the edge, or from the high point on one side of a coin or medal to the high point on the opposite side. Thickness is the third dimension of a numismatic item, height and width are the first two (or, in the case of a circular item, diameter is the first dimension, thickness is the second). Thickness is always measured in millimeters although it is sometimes expressed in inches.

For all struck pieces thickness is formed by the gauge of metal of the blank it is struck from. Blanks are cut from rolled strip and strip can be rolled to any dimension. Thickness is altered slightly by striking: the amount of relief of the die may alter the thickness (deeper relief, of course, creates greater thickness). Thus thick or thin struck pieces are usually a direct result of the rolled stock that is thicker or thinner than prescribed gauge.

It is called gauge before the coin or medal is struck, it is called thickness after it is struck.

Coin thickness.  For coins the rolled stock is called thickness strip when it is the correct thickness to be blanked for a certain coin. Modern rolling mills have automatic micrometers that monitor the thickness after each pass through the mills. Thus the strips are rolled until a preset thickness is reached.

For example the composition of United States dimes, quarters and half dollars are the same. Half dollar thickness strip is rolled to one prescribed thickness, quarter stock

is rolled to a thinner strip, dime stock to even less. These thickness strips must be fed into the a blanking press with blank dies of the diameter to match the denomination's thickness.

Special coins of double thickness, or multiple thickness, are known as

piedfort. Very thick coins, usually of crude design or manufacture, are called dumps.

Medal thickness.  In practice of striking art medals, choosing the proper gauge is the responsibility of the press foreman. He examines the amount of relief (how deep the relief is in the die) and estimates how many blows will be required to fully bring up that relief, then chooses the proper gauge blank stock to accomplish that relief. Also – and of great importance – it cannot be too thin a blank or this will break dies quicker; thicker blanks reduce the chance of dies breaking. However, and particularly for precious metals, thicker blanks increase costs of the material. Prescribed gauge is an attempt to control cost and to insure a precise precious metal content.

In the late 20th century German technology is so great that manufacturers there can control the thickness of a blank and then strike a piece to a prescribed weight in addition to a prescribed gauge. Bullion coins and medals, for example, are often required to be a prescribed weight, precisely one ounce, or 1000-gram for example. An exact diameter is chosen, the piece is blanked to the exact weigh tolerance, and when struck the weight is exactly the weight required. Manufacturers in other parts of the world have chosen German-made equipment for this precision.

Thickness anomalies.  Too thick or too thin a struck coin is usually a human error, a press operator who feeds an incorrect thickness strip into his blanking press. It is more likely this happens than for a rolling press to roll an incorrect gauge.

Cataloging.  In numismatic cataloging, diameter and weight of an individual specimen is more important than its thickness. Thickness is recorded only when it deviates from the normal. Even then it is usually called thick or thin, without expressing an exact thickness (as measured in millimeters). There are several reasons for this: (1) it is not as dramatic a difference as, say, a die variety; (2) in normal production there is a natural deviation of slight thickness in all struck pieces; and (3) the ease of making slight differences in rolled strip before the blank is made.

When thickness is measured, it is done at the edge for coins (which should be the greatest distance).  High relief medals could be measured from the high point of one side to the high point of the opposite side, but here, again, this is seldom done. (It is for this reason of where to measure – because of the existence or lack of the rim or the modulated relief – that any thickness measurement lacks scientific exactitude for medals.)

See gauge, Measurements and Weights (Appendix 5).

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators


Roger W. Burdette, Editor

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