The energy spectrum of ultra-high energy cosmic rays ( UHECRs ) is discussed on the basis of the Yakutsk array database analysis .
In the region E _ { 0 } = 10 ^ { 17 } to 3 \times 10 ^ { 19 } eV the showers are detected under trigger-500 , while at energies above 3 \times 10 ^ { 19 } eV the whole acceptance area for trigger-1000 is used in order to utilize all the data available in the region of Greisen-Zatsepin-Kuzmin ( GZK ) cutoff .
Updated relations are adapted to estimate the primary energy having detected densities of charged particles at the distance 300/600 m from the shower axis .