Franklin to Coulomb Converter

About this calculator

The franklin (Fr), also called the statcoulomb (statC or esu), is the unit of electric charge in the old CGS-esu (centimeter-gram-second, electrostatic) system of units, defined so that two equal point charges of 1 franklin placed 1 centimeter apart in a vacuum repel each other with a force of exactly 1 dyne. It predates the modern SI system, where charge is measured in coulombs, and the two units relate by the exact factor 1 Fr = 3.335640951982×10⁻¹⁰ C, tied directly to the speed of light through the CGS-to-SI conversion.

This converter switches electric charge between franklins and coulombs in either direction. It's mainly needed by physicists and historians of science reading older electromagnetism literature — many 19th and early 20th-century papers, and some physics textbooks that still favor Gaussian/CGS units for elegance in Maxwell's equations, report charge in franklins or statcoulombs, and converting them to coulombs is necessary to compare with modern SI-based results.