The Hubble diagram (HD) is a plot that contains a luminous distance modulus presented with respect to the redshift. The distance modulus–redshift relation of the most well-known “standard candles”, the type Ia supernovae (SN), is a crucial tool in cosmological model testing. In this work, we use the SN Ia data from the Pantheon catalogue to calibrate the Swift long gamma-ray bursts (LGRBs) as “standard candles” via the Amati relation. Thus, we expand the HD from supernovae to the area of the Swift LGRBs up to z ∼ 8. To improve the quality of estimation of the parameters and their errors, we implement the Monte-Carlo uncertainty propagation method. We also compare the results of estimation of the Amati parameters calibrated by the SN Ia, and by the standard ΛCDM model and find no statistically significant distinction between them. Although the size of our LGRB sample is relatively small and the errors are high, we find this approach of expanding the cosmological distance scale promising for future cosmological tests.