Diameters of Modern Coins for Comparison

U.S. Coins		Euro Coins
U.S. Half dollar	30.5 mm	2 euro	25.75 mm
U.S. Quarter	24.1 mm	1 euro	23.25 mm
U.S. Dime	17.9 mm	50 eurocent	24.25 mm
U.S. Nickel	21.3 mm	20 eurocent	22.25 mm
U.S. Penny	18.9 mm	10 eurocent	19.75 mm
		5 eurocent	21.75 mm
		2 Eurocent	18.75 mm
		1 Eurocent	16.25 mm
U.K. Coins
2 Pounds	28.4 mm
1 Pound	22.5 mm
Fifty pence	27.3 mm (7 sided)
Twenty Pence	21.4 mm (7 sided)
Ten Pence	24.5 mm
Five pence	18 mm
Two pence	26 mm
One pence	20 mm

Diameter 101

The Diameter of ancient coins is usually expressed in millimeters. In FORVM’s catalog descriptions you will usually find the coin’s weight, then diameter, followed by the die axis. Since many Americans are not familiar with millimeters and because it can help anyone visualize size better, we provide comparisons to modern coins below.

Diameters of Modern Coins for Comparison

U.S. Coins		Euro Coins
U.S. Half dollar	30.5 mm	2 euro	25.75 mm
U.S. Quarter	24.1 mm	1 euro	23.25 mm
U.S. Dime	17.9 mm	50 eurocent	24.25 mm
U.S. Nickel	21.3 mm	20 eurocent	22.25 mm
U.S. Penny	18.9 mm	10 eurocent	19.75 mm
		5 eurocent	21.75 mm
		2 Eurocent	18.75 mm
		1 Eurocent	16.25 mm
U.K. Coins
2 Pounds	28.4 mm
1 Pound	22.5 mm
Fifty pence	27.3 mm (7 sided)
Twenty Pence	21.4 mm (7 sided)
Ten Pence	24.5 mm
Five pence	18 mm
Two pence	26 mm
One pence	20 mm