The proton is the subatomic particle that carries one positive elementary charge.
Protons are found in the nuclei of atoms, together with neutrons. Their positive charge is equal in magnitude to the negative charge of an electron. The number of protons in an atom determines which chemical element it is: hydrogen has one proton, helium has two, and carbon has six.
A proton is not elementary; it is a composite particle made of three valence quarks—two up quarks and one down quark—bound by the strong interaction. Quarks also carry fractional electric charges, but their combination gives the proton a net charge of +1 elementary charge.
The neutron is similar in mass but electrically neutral, while the electron has the opposite charge. The proton’s charge is approximately 1.602 × 10−19 coulombs, a value used to define the elementary charge in the International System of Units.