This is a brief and rather simplified guide to the weights of authentic examples of some of the ancient coin types which are popular with collectors, fakes of which, in my opinion, you are quite likely to encounter on eBay. If the relevance of this subject is not obvious to you then  please refer to my other guide HOW TO AVOID FAKE ANCIENT COINS ON EBAY. Rather than relying on the standard textbook weights, I have taken the lowest and highest weights from a large number of examples in the auction catalogues of the Classical Numismatic Group, a major auction house specializing in top quality material. Genuine coins will doubtless exist just below or above the weight ranges given below but cautious collectors will fix their sights on the mean for each type  (never forgetting that the clever fakers will go to the trouble of getting their weights right.) You should avoid bidding on examples which fall outside their range - do not give them the benefit of the doubt.

Athens  Athena/owl tetradrachms 16.5-17.25g

Athens new style tets 16.5-17g   (tet = tetradrachm)

Macedon Philip II tets 13.5-14.5g

Alexander the Great tets 16-17.3g

Lysimachos tets 16-17.3g

Seleukid/Baktrian/Indo-Greek tets  3rd-2nd c. BC 16-17.25g (Attic standard)

Seleukid tets 1st c. BC 15.5-16g (Attic standard)

Baktrian/Indo-Greek tets 1st c. BC 9-10g

Ptolemaic/Seleukid tets (Phoenician standard) 13.5-15.5g

Kyme/Myrina tets 16-17g

Syro-phoenician tets: 1st c.AD 13.5-15.25g    2nd c.AD 13-15g   3rd c. AD 11-14g

Sestertius 1st c.AD 22-30g    2nd c.AD 17-28g    3rd c.AD 15-26g

Denarius  Republic 3.5-4g    Augustus-100AD 3-4g    2nd c.AD 2.5-3.5g    3rd c.AD. 2.3-3.5g

Antoninianius  Early-mid 3rd c. AD 4-5.5g    After 250AD 2-5g

Aureus 1st-early 3rd c.AD 7-8g    Mid 3rd c.AD 5-7g    Late 3rd c.AD 4.5-5.5g

Solidus  4th-5th c.AD  4-4.5g

If anyone believes I have missed out an important type of which fakes frequently appear on eBay please let me know and I will add it.