To calculate Planck's constant using stopping potential and threshold frequency, the relationship E=hf is essential, where hf equals the maximum kinetic energy plus the work function. The maximum kinetic energy can be expressed as Kmax=eV, linking it to the stopping potential. A graph plotting stopping potential against frequency can help determine Planck's constant from the slope, which represents the energy conversion of the electron into photon energy. The threshold frequency indicates where the stopping potential reaches zero, providing a crucial reference point. Ultimately, the calculation requires understanding the relationship between kinetic energy, stopping potential, and frequency.