  We theoretically and experimentally study the universal scaling property of
the spin-1/2 Kondo state in the magnetic field dependence of bias-voltage
linear conductance through a quantum dot at low temperatures. We discuss an
efficient and reliable procedure to evaluate the Kondo temperature defined at
the ground state from experimental or numerical data sets of the magnetic field
dependence of the linear conductance or the magnetization of the quantum dot.
This procedure is helpful for quantitative comparison of the theory and the
experiment, and useful in Kondo-correlated systems where temperature control
over a wide range is difficult, such as for cold atoms. We demonstrate its
application to experimentally measured electric current through a carbon
nanotube quantum dot.
