A measurement of mass used for elementary particles. The formula is 1 billion (G) electron volts (eV) divided by (over) the speed of light (c) squared. This measurement equals about 1.78 x 10^-36 kg (3.92 x 10^-36 lb). Following is a chart of some elementary particles and their mass:

```Up Quark:                .0015 to .005
Down Quark:              .003 to .009
Strange Quark:           1.1 to 1.4
Charm Quark:             .06 to .17
Bottom (beauty) Quark:   4.1 to 4.4

Photon:                  0?
Gluon:                   0?
W+:                      80
W-:                      80
Z:                       91

Proton:                  .938
Neutron:                 .940
Sigma+:                  1.189
Sigma-:                  1.193
Lamda+-:                 1.116

Pion+:                   .14
Pion+-:                  .135
Pion-:                   .14
Kaon+:                   .494
Kaon-:                   .494
D+:                      1.869
D-:                      1.869```

Thanks to Chen Ning Yang for the table.