The Roman as or æs was called so because it was made of brass.

ATTIC MEASURES OF CAPACITY FOR THINGS LIQUID, REDUCED TO THE ENGLISH WINE MEASURE.
gals.pts.sol.
in.		dec.
Cochlearion  01⁄120003565⁄12
   2Cheme  01⁄6000712⅝
   2½   1¼Mystron  01⁄48008911⁄48
   5   2½   2Conche  01⁄24017811⁄24
  10   5   4   2Cyathus  01⁄12035611⁄12
  15   7½   6   3  1½Oxybaphon  0⅛0335⅜
  60  30  24  12  6  4Cotyle  0½2141½
 120  60  48  24 12  8  2Xestes  014283
 720 360 388 144 72 48 12 6Chous  0625698
86404320345617288645761447212Metretes 10219626
ROMAN MEASURES OF CAPACITY FOR THINGS LIQUID, REDUCED TO ENGLISH WINE MEASURE.
gals.pts.sol.
in.		dec.
Ligula  01⁄4801176⁄12
    4Cyathus  01⁄120469⅔
    6    1½Acetabulum  0⅛0704½
   12    3   2Quartarius  0¼1409
   24    6   4   2Hemina  0½2818
   48   12   8   4   2Sextarius  015636
  288   72  48  24  12  6Congius  074942
 1152  288 192  96  48 24  4Urna  34½533
 2304  576 384 192  96 48  8 2Amphora  711066
46080115207680384019209601604020Culeus143311095

N.B. The quadrantal is the same as the amphora. The Cadus, Congiarius, and Dolium denote no certain measure. The Romans divided the Sextarius, like the libra, into 12 equal parts, called Cyathi, and therefore their calices were called sextantes, quadrantes, trientes, &c., according to the number of cyathi which they contained.

ATTIC MEASURE OF CAPACITY FOR THINGS DRY, REDUCED TO ENGLISH CORN MEASURE.
pecks.gals.pts.sol.
in.		dec.
Cochlearion00002767⁄20
   1Cyathus0002763½
  15  1½Oxybaphon0004144¾
  60  6  4Cotyle00016579
 120 12  8  2Xestes00033158
 180 18 12  3 1½Chœnix00115705¾
80408645761447248Medimnus4063501

N.B. Besides this Medimnus, which is the Medicus, there was a Medimnus Georgicus, equal to six Roman Modii.