Going by diameter, my Salus Vespasian is the largest at 20mm, while Vesta Julia Domna is only 15mm! if you have chunky denarius and a one thin as a foil, feel free to post them as well.
I do not have this Antony in hand today but it is only 3.0g and thin. I suspect it was struck on an earlier coin that had been hammered flat. Small coins require deciding if the size is original or the result of wear or damage. Your Julia Domna come from a period known for sub-standard size coins. My is large for these and odd for the reverse SANCTAS spelling. Official?
An interesting question I've never thought about, and the answers I found (by scrolling through my personal coin catalog) surprised me a little. Largest in diameter: Julia Paula (21 mm) and Julia Mamaea (20.5 mm.) Oddly enough, they're both very much on the light side (2.49 and 2.88 g., respectively), although not my lightest. Smallest flan in diameter: L. Roscius Fabatus serrate denarius (Juno Sospita/Maiden feeding snake), 16 mm. (but 3.93 g.) It looks like it was probably clipped around the rim. Heaviest in grams: L. Piso Frugi (Apollo/horseman) (4.02 g.) and Aulus Plautius (Cybele/Bacchius Judaeus with camel) (4.25 g.). Lightest in grams: I have a half-dozen between 2.49 and 3.0 g., but the two lightest by quite a bit are my denarii of Macrinus (1.58 g.) and Maximus Caesar (son of Maximinus Thrax) (1.7 g.) Both are 19 mm. in diameter. @dougsmit and @JayAg47, does any of this have any significance? I have no idea, although I remember wondering when I bought the last two why they were so light.
The largest you will find will almost certainly come from the very first issue during the Second Punic War. They were a nominal 4.5g or 4 scruples. The Story of the Coin Struck to Fight Hannibal: The First Denarius and its Influence Roman Republic Second Punic War (218 – 201 BC) Anonymous AR Denarius, Rome Mint, struck ca. 211 BC Wt.: 4.2 g Dia.: 20 mm Obv.: Helmeted head of Roma right. X in left field Rev.: Dioscuri galloping right. ROMA in exergue and partially incuse on raised tablet Ref.: Crawford 44/5. Sydenham 167. RBW 169. Ex Numismatic Ars Classica Auction 100 Part II, Lot 1368 (May 30, 2017) My lightest coin that could unambiguously be called a denarius is probably this one. Roman Empire Geta as Caesar AR Denarius, Rome mint, struck ca. AD 198-200 Dia.: 18 mm Wt.: 2.33 g Obv.: L SEPTIMIVS GETA CAES. Bareheaded and draped bust right. Rev.: FELICITAS TEMPOR. Felicitas standing left, holding caduceus and cornucopia. Ref.: RIC IVa 2 Ex AMCC 1 (Dec. 1, 2018) However, the 3rd century crises brought with it a lot of coin debasement and strict denominations become more complex to identify. These debased “denarii” if we can call them that can be pretty light sometimes. ALL Ancient Coins are Worthy of Study Roman Empire Aurelian (AD 270-275) AE Denarius, Rome mint, 1st officina Dia.: 18.5 mm Wt.: 2.2 g Obv.:IMP AVRELIANVS AVG; Laureate, draped bust right. Rev.: VICTORIA AVG; Victory walking left, holding wreath and palm, captive at food left. A in exergue Ref.: RIC V-a 73 Roman Empire Aurelian (AD 270-275) Dia.: 18.2 mm Wt.: 1.5 g Obv.: Radiate, draped bust right. Rev.: IOVI CON-SER (?); Emperor standing right, (holding sceptre?), receiving globe from Jupiter, standing left holding sceptre.
The coin pictured below is not in my collection, however, it caught my attention last week in CNG 115 auction, lot 553. The coin is 19 mm in dia., but weighs 4.65 gm ! It sold for $720.00. Roman Republic, C. Antonius Balbus, 83-82 BC, AR Denarius, Rome Mint.
Here's a 6.9mm diameter difference in a pair of denarii. One is 3.87 grams The other is 3.88 grams. One is 15.4 mm The other is 22.3 mm. One is L. Julius L.f. Caesar, 103 BC, AR denarius Obv: Helmeted head of Mars left; retrograde B• above Rev: Venus Genetrix driving biga left, drawn by two Cupids; lyre before them, retrograde B• above Ref: Crawford 320/1; Sydenham 593a; Julia 4a L. Julius L.f. Caesar a relative of Julius Caesar the dictator one of the earliest members of the family to attain the consulship governor of Macedonia in 94 BC consul during the Social War passed the basic law which offered Roman citizenship to the Italian allies opponent of Marius killed when Marius returned to Rome in 87 BC grandfather of Mark Antony The other is Lucius Caesius, 112-111 BC, AR Denarius, Rome mint Obv: Youthful, diademed and draped bust of Vejovis left, seen from behind, hurling thunderbolt with right hand; monogram to right Rev: Two Lares seated right on rock, each holding a spear in left hand; dog between them, the Lar on right petting head of dog with right hand; head of Vulcan and tongs above; (E retrograde)R monogram to right; L • CÆSI in exergue Ref: Crawford 298/1; Sydenham 564; Caesia 1 Both are RR denarii from the end of the 2nd century BC.