Extended human-scale weights and measures

Delta's D&D blog has brought it to my attention that stone units make a simple and convenient way of estimating encumbrance. He has a very good point, but sooner or later the situation will arise when we want to know weights to greater precision than multiples of 14 English pounds. This information helps to put you inside the heads of the locals. You never know when you might need to make conversions.

Here's an idea. A stone is close enough to 25 "marks" in the Troy system of weights that it makes no difference. By definition, each mark  is divided into 8 troy ounces. This seems granular enough. Incidentally, this make four stones into almost exactly 100 marks, which is certainly convenient. We can call 100 marks a "talent," because it's approximately one Attic talent, the weight of a cubic foot of water. Thus, we can also define a mark as approximately 1% of the weight of a cubic foot of water, if you care about details like that.

Marks and ounces are the right size for food. A mark is the weight of a typical loaf of hearty brown bread, and one ounce is about the weight of a slice from that loaf. However, most heavy (dense) things smaller than one mark are measured in 1/5's of a troy ounce, which is a standard coinweight or "piece." This weight falls between that of a US quarter and the new dollar coin. Thus, a heavy sack of 1000 standard coins weighs one stone. This ratio is more realistic and convenient than the official ratio of 10 to the pound (which requires some very large coins). This is, of course, another advantage of using stone units.

As for pounds, I don't believe you should use them. Fantasy units of measurement should be somewhat exotic and not too well defined. But for those of you that must have your weights in pounds, let's define a "compromise pound" as one-hundredth part of an English hundredweight (that is, 1.12 English pounds, close to a metric pound), which is two marks. Convert a number from marks to pounds by halving it.


Table 1

1 talent = 4 st = 50 lb = 100 mk = 800 ozt (= 56 lbs avoirdupois, 25 kg)
1 stone = 25 mk = 200 ozt = 1000 pc (= 224 oz avoirdupois, 6.25 kg)

1 pound = 2 mk =  16 ozt = 80 pc (=1 T lb, 13.4 oz avoirdupois, 500 g)
1 mark = 1/2 lb = 8 ozt = 40 pc (= 2/3 T lbs, 6.7 oz avoirdupois, 250 g)

1 troy ounce = 5 pc (= 480 gr, 20 dwt, 31.25 g)
1 coinweight = 1/5 ozt (= 96 gr, 5 dwt, 6.25 g)


Table 2

   0.0125 mk = 1/2 pc
   0.025 mk = 1 pc
   0.05 mk = 2 pc
   0.1 mk = 4 pc
   0.2 mk = 8 pc
   0.5 mk = 1/4 lb
   1.0 mk = 1/2 lb
   2.0 mk = 1 lb
   6.0 mk = 3 lb
  10.0 mk = 5 lb
  25.0 mk = 1 st
  50.0 mk = 2 st
 100.0 mk = 4 st
 250.0 mk  = 10 st
 500.0 mk = 5 tlt
1000.0 mk = 10 tlt
2500.0 mk = 25 tlt
5000.0 mk = 50 tlt