  We use a hybrid approach that combines high-resolution simulations of the
formation of a Milky Way-like halo with a semi-analytic model of galaxy
formation to study the mass content of dwarf galaxies in the concordance
$\Lambda$CDM cosmology. We find that the mass within 600 pc of dark matter
haloes hosting luminous satellites has a median value of $\sim 3.2\times 10^7$
Msun with very little object-to-object scatter. In contrast, the present day
total luminosities of the model satellites span nearly five orders of
magnitude. These findings are in very good agreement with the results recently
reported in the literature for the dwarf spheroidal galaxies of the Milky Way.
In our model, dwarf irregular galaxies like the Small Magellanic Cloud, are
predicted to have similar or slightly larger dark matter mass within 600 pc.
