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Index Of All Titles


Aes Grave
Aes Rude
The Age of Gallienus
Alexander Tetradrachms
Ancient Coin Collecting 101
Ancient Coin Prices 101
Ancient Coin Dates
Ancient Coin Lesson Plans
Ancient Coins & Modern Fakes
Ancient Counterfeits
Ancient Glass
Ancient Oil Lamps
Ancient Weapons
Ancient Wages and Prices
Ancient Weights and Scales
Anonymous Folles
Anonymous Follis
Anonymous Class A Folles
Antioch Officinae
Armenian Numismatics Page
Byzantine Denominations
A Cabinet of Greek Coins
Caesarean and Actian Eras
Campgates of Constantine
A Case of Counterfeits
Byzantine Christian Themes
Clashed Dies
Coins of Pontius Pilate
Conditions of Manufacture
Corinth Coins and Cults
Countermarked in Late Antiquity
Danubian Celts
Damnatio Coinage
Damnatio Memoriae
Denarii of Otho
Diameter 101
Die Alignment 101
Dictionary of Roman Coins
Doug Smith's Ancient Coins
Edict on Prices
ERIC - Rarity Tables
Etruscan Alphabet
The Evolving Ancient Coin Market
Facing Portrait of Augustus
Fel Temp Reparatio
Fertility Pregnancy and Childbirth
Friend or Foe
The Gallic Empire
Gallienus Zoo
Greek Alphabet
Greek Dates
Greek Coin Denominations
Greek Mythology Link
Greek Numismatic Dictionary
Hellenistic Names & their Meanings
Hasmonean Dynasty
Helvetica's ID Help Page
The Hexastyle Temple of Caligula
Historia Numorum
Horse Harnesses
Identifying Ancient Metal Arrowheads
Illustrated Ancient Coin Glossary
Important Collection Auctions
Islamic Rulers and Dynasties
Kushan Coins
People in the Bible Who Issued Coins
Imperial Mints of Philip the Arab
Later Roman Coinage
Latin Plurals
Latin Pronunciation
Library of Ancient Coinage
Life in Ancient Rome
List of Kings of Judea
Malloy Weapons
Maps of the Ancient World
Military Belts
Mint Marks
Museum Collections Available Online
Nabataean Alphabet
Nabataean Numerals
The [Not] Cuirassed Elephant
Not in RIC
Numismatic Bulgarian
Numismatic Excellence Award
Numismatic French
Numismatic German
Numismatic Italian
Numismatic Spanish
Parthian Coins
Patina 101
Paleo-Hebrew Alphabet
Phoenician Alphabet
Pi-Style Athens Tetradrachms
Pricing and Grading Roman Coins
Reading Judean Coins
Representations of Alexander the Great
Roman Coin Attribution 101
Roman Militaria
Roman Mints
Roman Names
Rome and China
Satyrs and Nymphs
Serdi Celts
The Sign that Changed the World
Silver Content of Parthian Drachms
Star of Bethlehem Coins
Statuary Coins
Sylloge Nummorum Graecorum
Syracusian Folles
Taras Drachms with Owl Left
The Temple Tax Hoard
Test Cut
Travels of Paul
Tribute Penny
Tribute Penny Debate Continued (2015)
Tribute Penny Debate Revisited (2006)
Tyrian Shekels
Uncleaned Ancient Coins 101
Venus Cloacina
What I Like About Ancient Coins
Who was Trajan Decius
Widow's Mite

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Diameter 101

The diameter of ancient coins is usually expressed in millimeters. In Forumís catalog descriptions you will usually find the coinís weight, then maximum diameter, followed by the die axis.

The ancient denomination names and values of some late Roman bronze coins are uncertain. Often they are referred to with the following size (diameter) designations:
AE1 = over 25mm
AE2 = 21mm Ė 25mm
AE3 = 17mm Ė 21mm
AE4 = less than 17mm 

The denomination of a coin is based on the usual size for the type.  The coins were handmade and the same type can vary significantly in size.  Some individual coins that are larger or smaller than usual for their type will be outside the parameters above.

We also do not know the names of the denomination or value of many Greek and Roman provincial coins. Often the denomination given for these types is simply AE, indicating a base metal or alloy, mostly copper, followed by the diameter in millimeters. An AE23 is a base metal (copper, bronze, brass, base billon, or potin) coin with a 23 millimeter diameter.

Diameters of Modern Coins for Comparison

Since many Americans are not familiar with millimeters and because it can help anyone visualize size better, we provide comparisons to modern coins below.

U.S. Coins


Euro Coins

U.S. Half dollar30.5 mm 2 Euro25.75 mm
U.S. Quarter  24.1 mm 1 Euro23.25 mm
U.S. Dime    17.9 mm 50 Eurocent24.25 mm
U.S. Nickel 21.3 mm 20 Eurocent22.25 mm
U.S. Penny   18.9 mm 10 Eurocent19.75 mm
   5 Eurocent21.75 mm
   2 Eurocent18.75 mm
   1 Eurocent16.25 mm

U.K. Coins

2 Pounds28.4 mm   
1 Pound22.5 mm   
Fifty pence27.3 mm (7 sided)   
Twenty Pence21.4 mm (7 sided)   
Ten Pence24.5 mm   
Five pence18 mm   
Two pence 26 mm   
One pence20 mm

Inch and Millimeter Equivalents

Divide millimeter lengths by 25.4 to determine the inch length.

Approximate Size In Inches
Precise Size In Inches
1/32 Inch
0.03937 Inches
1/16 Inch
0.07874 Inches

3/32 Inch

0.11811 Inches
1/8 Inch
0.15748 Inches
3/16 Inch
0.19685 Inches
Almost 1/4 Inch
0.23622 Inches
Little over 1/4 Inch
0.27559 Inches
5/16 Inch
0.31496 Inches
Almost 3/8 Inch
0.35433 Inches
Little over 3/8 Inch
0.39370 Inches
7/16 Inch
0.43307 Inches
Almost 1/2 Inch
0.47244 Inches
Little over 1/2 Inch
0.51181 Inches
9/16 Inch
0.55118 Inches
Almost 5/8 Inch
0.59055 Inches
5/8 Inch
0.62992 Inches
Almost 11/16 Inch
0.66929 Inches
Almost 3/4 Inch
0.70866 Inches
Little over 3/4 Inch
0.74803 Inches
Almost 13/16 Inch
0.78740 Inches
Little over 13/16 Inch
0.82677 Inches
Almost 7/8 Inch
0.86614 Inches
Little over 7/8 Inch
0.90551 Inches
15/16 Inch
0.94488 Inches
1 Inch
0.98425 Inches

Table for Converting English Inches into Millimeters and the Measures of the Mionnet's Scale

- 101

Ancient Coin Collecting 101
Uncleaned Ancient Coins 101
Roman Coin Attribution 101
Greek Coin Collecting 101
Patina 101
Magnification 101
Die Alignment 101
Bust Types 101
Ancient Coin Prices 101