MEASUREMENTS UNITS  MASS
Mass (kilogram): The
kilogram is the unit of mass. It is equal to the mass of
the
International prototype of the kilogram (a
platinumiridium alloy cylinder) kept at BIPM, the International Bureau of Weights and Measures in
Sèvres, Paris. It consists of an alloy of 90 % platinum
10 % iridium, and was made in 1879 by George Matthey, of
Johnson Matthey, in the form of a cylinder, 39 mm high and
39 mm diameter. It is stored at atmospheric pressure in a
specially designed triple belljar.
Mass is denoted by kg
For all practical purposes Conventional Mass is related
to Mass via the following equation:
where:

M_{c}
is the conventional mass value

M
is the mass value

is the density of the test weight material in kg·m^{3}
Units of mass
There have historically been four different English
systems of mass: Tower weight, Troy weight, avoirdupois
weight, and apothecaries weight. Tower weight fell out of
use (due to legal prohibition) centuries ago, and was
never used in the United States. Troy weight is still used
to weigh precious metals. Apothecaries weight, once used
in pharmacy, has been largely replaced by metric
measurements. Avoirdupois weight is the primary system of
mass in the U.S. customary system.
The Avoirdupois units are legally defined as measures
of mass, but the names of these units are sometimes
applied to measures of force. For instance, in most
contexts, the pound avoirdupois is used as a unit of mass,
but in the realm of physics, the term "pound" can
represent "poundforce" (a unit of force properly
abbreviated as "lbf").
English Standards of weight
Avoirdupois weight
27.344 grains 
= 
1 dram 
16 drams 
= 
437 ½ grains 
16 ounces 
= 
7000 grains 
14 pounds 
= 
1 stone 
28 pounds 
= 
1 quarter 
4 quarters 
= 
112 pounds 
20 hundredweights 
= 
2240 pounds 
3 pennies 
= 
5 halfpennies 
4 grains 
= 
1 carat 
24 grains 
= 
1 pennyweight 
20 pennyweights 
= 
480 grains 
12 troy ounces 
= 
5760 grains 
The ton and hundredweight above are referred to as the
short ton, and the short hundredweight, to
distinguish them from the British Imperial ton and
hundredweight, which are larger and hence are referred to
as the long ton and long hundredweight. The
long ton has limited use in the United States.
 1 long hundredweight = 112 lb ≈ 50.802 kg
 1 long ton = 20 long cwt = 2240 lb ≈ 1016.047 kg ≈
1.016 t
Apothecaries' weight
The grain has the same definition as for avoirdupois
weight.
 1 scruple (s ap) = 20 gr ≈ 1.296 g
 1 dram apothecaries (dr ap) = 3 s ap ≈ 3.888 g
 1 ounce apothecaries (oz ap) = 1 oz t = 8 dr ap =
480 gr ≈ 31.103 g
 1 pound apothecaries (lb ap) = 1 lb t = 12 oz ap =
5760 gr ≈ 373.242 g
The pound and ounce apothecaries are identical to the
pound and ounce troy.
Troy weight
The grain has the same definition as for Avoirdupois
weight.
 1 pennyweight (dwt) = 24 gr ≈ 1.555 g
 1 ounce troy (oz t) = 20 dwt = 480 gr ≈ 31.103 g
 1 pound troy (lb t) = 12 oz t = 5760 gr ≈ 373.242 g
Metric Standards of weight
Weight
1 grain (avoirdupois and troy) 
= 
0.0648 grammes 
1 pennyweight 
= 
1.5552 grammes 
1 dram (avoirdupois) 
= 
1.772 grammes 
1 ounce (16 drams) 
= 
28.350 grammes 
1 ounce (troy and apothecary) 
= 
31.1035 grammes 
1 pound (16 ounces) 
= 
0.45359 kilogram 
1 hundredweight 
= 
112 pounds 
1 British ton 
= 
2240 pounds 
1 American ton 
= 
2000 pounds 
1 milligram 
= 
0.015 grain 
1 gramme 
= 
15.432 grains 
1 kilogram 
= 
2.20462 pounds 
1 quintal 
= 
100 kilograms 
1 tone 
= 
0.9842 British ton 
1 gallon of water at 62˚F 
= 
10 lb 
1 cubic foot water at 60˚F 
= 
62.37 lb 
1 cubic inch water at 60˚F 
= 
0.0361 lb 
24 hours 
= 
1440 min 
12 hour 
= 
720 
1 metre 
= 
3 ft 3 in. 
Distinctive Masses of Certain Objects
Object 
Mass
(Kg) 
Electron 
10^{30} 
Proton 
10^{27} 
Uranium
atom 
10^{25} 
Red blood
cell 
10^{13} 
Dust
Particles 
10^{9} 
Rain Drop 
10^{6} 
Mosquito 
10^{6} 
Grape 
10^{3} 
Human 
10^{2} 
Automobile 
10^{3} 
Boeing
747 air craft 
10^{6} 
Moon 
10^{23} 
Earth 
10^{25} 
Sun 
10^{30} 
Milky Way
galaxy 
10^{41} 
Observable Universe 
10^{55} 
