We report about a photometric campaing of the local active galactic nuclei (AGN) 3C120. The broad line region (BLR) size and the host-subtracted AGN luminosity were obtained through photometric reverberation mapping. The Hβ emission line responds to continuum variations with a rest frame lag of 23.6 ± 1.69 days. Using the flux variation gradient (FVG) method we determined the host galaxy subtracted rest frame 5100Å luminosity at the time of our monitoring campaign with an uncertainty of 10% (LAGN = (6.94 ± 0.71) × 1043erg s-1). Compared with recent spectroscopic reverberation results, 3C120 shifts in the RBLR-LAGN diagram remarkably close to the theoretically expected relation of R L0.5. This campaign is part of an ongoing photometric survey of Seyfert 1 galaxies conducted with robotic telescopes located near Cerro Armazones in Chile.