The strong coupling constant is computed from three-loop lattice perturbation theory for eight Wilson loops and six Creutz ratios. Three lattice spacings of the MILC 2+1 unquenched lattice data sets were used to perform a continuum extrapolation and estimate the higher order corrections. The light quark mass dependence is shown to be negligible. The static potential at two-loops for R / a ⩽ 3 was used as a cross-check. The preliminary result is α MS ¯ ( M Z ) = 0.1175 ( 15 ) , which improves on the 2004 PDG world-average of 0.1187(20).