Context : Magnetic Bright Points ( MBPs ) are small-scale magnetic features in the solar photosphere .
They may be a possible source of coronal heating by rapid footpoint motions that cause magnetohydrodynamical waves .
The number and size distribution are of vital importance in estimating the small scale-magnetic-field energy .

Aims : The size distribution of MBPs is derived for G-band images acquired by the Hinode/SOT instrument .

Methods : For identification purposes , a new automated segmentation and identification algorithm was developed .

Results : For a sampling of 0.108 arcsec/pixel , we derived a mean diameter of ( 218 \pm 48 ) km for the MBPs .
For the full resolved data set with a sampling of 0.054 arcsec/pixel , the size distribution shifted to a mean diameter of ( 166 \pm 31 ) km .
The determined diameters are consistent with earlier published values .
The shift is most probably due to the different spatial sampling .

Conclusions : We conclude that the smallest magnetic elements in the solar photosphere can not yet be resolved by G-band observations .
The influence of discretisation effects ( sampling ) has also not yet been investigated sufficiently .