  The creep motion of domain walls driven by external fields in magnetic thin
films is described by universal features related to the underlying depinning
transition. One key parameter in this description is the roughness exponent
characterizing the growth of fluctuations of the domain wall position with its
longitudinal length scale. The roughness amplitude, which gives information
about the scale of fluctuations, however, has received less attention. Albeit
their relevance, experimental reports of the roughness parameters, both
exponent and amplitude, are scarce. We report here experimental values of the
roughness parameters for different magnetic field intensities in the creep
regime at room temperature for a Pt/Co/Pt thin film. The mean value of the
roughness exponent is $\zeta = 0.74$, and we show that it can be rationalized
as an effective value in terms of the known universal values corresponding to
the depinning and thermal cases. In addition, it is shown that the roughness
amplitude presents a significant increase with decreasing field. These results
contribute to the description of domain wall motion in disordered thin magnetic
systems.
