  A global effort to redefine our International System of Units (SI) is
underway and the change to the new system is expected to occur in 2018. Within
the newly redefined SI, the present base units will still exist but be derived
from fixed numerical values of seven reference constants. More specifically,
the unit of mass, the kilogram, will be realized through a fixed value of the
Planck constant $h$. For instance, a watt balance can be used to realize the
kilogram unit of mass within a few parts in $10^8$. Such a balance has been
designed and constructed at the National Institute of Standards and Technology.
For educational outreach and to demonstrate the principle, we have constructed
a LEGO tabletop watt balance capable of measuring a gram size mass to 1 %
relative uncertainty. This article presents the design, construction, and
performance of the LEGO watt balance and its ability to determine $h$
