Galaxy number counts from Euclid observations. The galaxy differential number counts derived from the simulated Euclid observations in the I_E band of the six HFF parallel fields are shown by the grey histogram with error bars. For comparison, those measured from HST observations (Capak et al. 2007) are indicated by the black solid line. The vertical blue line marks the limiting magnitude in the I_E band (24.5 at 10 σ). The cumulative number of galaxies per arcmin² is shown by the red dashed line. We estimate the number counts from a total area of ∼32.67 arcmin². We quote the number of galaxies per arcmin² at the limiting magnitude at the top of the blue vertical line.