In this work, cryogenic hydrogen fires at various pressures and initial temperatures were investigated experimentally. The flame length, width, thermal radiation fluxes and flame temperatures in the down-stream region were measured for the scenarios with 1.6-3 mm jet nozzle, 133 to 273 K and 2-4 bar(abs). The results show that the flame size is related to not only the jet nozzle diameter but also the stagnation pressure and temperature. Under constant pressure, the flame size, total radiative power and radiation fraction increase with the decrease of temperature, due to lower choked flow velocity and higher density of cryogenic hydrogen. A correlation of normalized flame length L-f/d(j) is proposed based on the stagnation pressure of hydrogen p(0) and the ratio of ambient temperature and hydrogen stagnation temperature T-atm /T-0 . The results verify that such correlation can be used to a priori prediction of flame size at a wide variety of hydrogen temperatures (133 K similar to room temperature). Additionally, based on the reciprocal function, a correlation of the radiative fraction chi rad is presented as a function of global flame residence time tau(f). (C) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.