  We present size measurements of 78 high-redshift ($z\geq 5.5$) galaxy
candidates from the Reionisation Lensing Cluster Survey (RELICS). These distant
galaxies are well-resolved due to the gravitational lensing power of foreground
galaxy clusters, imaged by the Hubble Space Telescope (HST) and the Spitzer
Space Telescope. We compute sizes using the forward-modeling code Lenstruction
and account for magnification using public lens models. The resulting
size-magnitude measurements confirm the existence of many small galaxies with
effective radii $R_{\rm{eff}}<200$ pc in the early universe, in agreement with
previous studies. In addition, we highlight compact and highly star-forming
sources with star formation rate surface densities
$\Sigma_\text{SFR}>10M_\odot\text{yr}^{-1}\text{kpc}^{-2}$ as possible Lyman
continuum leaking candidates that could be major contributors to the process of
reionisation. Future spectroscopic follow-up of these compact galaxies (e.g.,
with the James Webb Space Telescope) will further clarify their role in
reionisation and the physics of early star formation.
