Precise determination ofTcin QCD from scaling

Existing lattice data on the QCD phase transition are analyzed in renormalized perturbation theory. In quenched QCD it is found that $T_c$ scales for lattices with only three time slices, and that $T_c/{\Lambda }_{\overline{\mathrm{MS}}}=1.15\mathrm{}\pm \mathrm{0.05.}$ A preliminary estimate in QCD with two flavors of dynamical quarks shows that this ratio depends on the quark mass. For realistic quark masses we estimate $T_c/{\Lambda }_{\overline{\mathrm{MS}}}=0.49\mathrm{}\pm \mathrm{0.02.}$ We also investigate the equation of state in quenched QCD at 1-loop order in renormalized perturbation theory.