The following is conversion table which uses grams (the most popular unit) as the common base for conversion.It provides a quick feel for the relative size of the various weighing units (arranged alphabetically):

 

 

To convert from grams to:

Abbreviation

multiply by

carats

ct

5.0

dram

dram

0.564383

grains

gn

15.432358

momme

mom

0.2666666

ounces

oz

0.0352739

pennyweights

dwt

0.6430149

pounds

lb

0.0022046

scruple

scruple

0.7716179

tael (Hong Kong)

tlh

0.0264554

tola (India)

tol

0.0857353

tael (Singapore)

tls

0.0264599

tael (Taiwan)

tlt

0.0266666

troy ounces

oz t

0.0321507

troy pounds

lb t

0.0026792

 

The grain (used in pharmacy and armaments) is the smallest shown (versus the gram) and the pound (used by your bathroom scale and your doctor) is the largest. Most of these units have extensive histories and logical reasons for coming into existence when they did. Many are hardly used at all in modern weighing, but all are still used in special areas. For instance, the pennyweight, whose name is derived from the weight of a British penny (defined as 1/240th of a pound sterling in the 18th Century), is still used commonly by Jewelers to weigh precious metals.Most dental labs use it to weigh the precious metals used in people dental devices.

Note that there are three different values and symbols used for the tael.Note also they are used in 3 different areas of theFar East.Note also that there values are very similar, withSingaporeandHong Kongbeing extremely close.History and politics provide the explanation, not necessity.

The troy system of pounds and ounces is believed to have originated in Troyes, Francein about the 5th century ad.There are 12 troy ounces to a troy pound; however, the troy pound is no longer used.On the other hand the troy ounce is commonly used to weigh gold and other precious metals and gemstones.If you purchase gold or other precious metals be sure you know which ounce you are paying for.The widely quoted price of gold is based upon the troy ounce, which is about 10% heavier than its Imperial (or Avoirdupois) cousin.

You would be hard put to find a woman who did not know that diamonds are her best friend and that they are weighed in carats. The name is believed to come from the Carob (a conifer tree) seed, as does the weight of 0.2 grams.There are, therefore, 5 carats to a gram (as shown in the table above).

The momme as a weight standard was developed inJapan.It is widely used to measure the weight of silk fabrics and, also, in the pearl industry.It has rarely even been heard of outside of these two industries, and is not used by consumers.

The metric system is becoming the de facto standard for most industrial applications and will probably, in time, become the sole standard.The resistance to it comes from niche industries who feel they benefit from the novelty of having a unique standard (like diamonds and precious metals).