This coin is not in RIC. The bust is almost identical to Rome 150 (H8 bust type), but the helmet on this coin is not laureate. It is an H4 bust and should be between Rome 149 and 150. No measurements.
Constantine I
A.D. 318-9
CONS-TANT- INVS AVG; helmeted and cuirassed bust left, holding spear pointing forward and shield on left arm.
ROMAE AETERNAE; Roma seated right, shield in lap inscribed X V; across fields P/R.
in ex. RP
RIC VII Rome --