A coulomb is the unit of electric charge in the International System of Units (SI) . It is defined as the amount of electricity that a 1-ampere (A) current carries in one second (s) . In the present version of the SI, one coulomb is equal to the electric charge delivered by a 1 ampere constant current in 1 second and to 5×10²⁷/801088317 elementary charges, e, (about 6.241509×1018 e) . The coulomb is named after Charles-Augustin de Coulomb, an 18th-19th century French physicist.

The charge of one coulomb is equivalent to the sum of the charges of 6.241 x 1018 electrons. The charge on one electron is 1.602 x 10-19 coulombs. The force with which two electrically charged bodies attract or repel one another depends on the product of their charges in coulombs, as well as on the distance between them.

Coulombs are used in calculations involving electrochemistry and by physicists studying electricity and magnetism.