In the phase diagram of carbon, the positions of the melting and thermodynamicequilibrium curves of detonation nanodiamonds or ultrafine diamonds are found as functions of diamond particle size. The position of the set of triple points located in the ranges of pressure 13.5-16.5 GPa and temperature 2210-4470 K and determining the region of the liquid state of nanocarbon is determined. In the phase diagram of nanocarbon, the diamond region is divided into three parts according to the type of nanoparticles: nanodiamond, liquid nanocarbon (nanodrops), and amorphous nanocarbon.