We report a measurement of the tt production cross section using the CDF II detector at the Fermilab Tevatron. The analysis is performed using 311  pb−1 of pp collisions at s√=1.96  TeV. The data consist of events selected with six or more hadronic jets with additional kinematic requirements. At least one of these jets must be identified as a b-quark jet by the reconstruction of a secondary vertex. The cross section is measured to be σtt=7.5±2.1(stat.)+3.3−2.2(syst.)+0.5−0.4(lumi.)  pb, which is consistent with the standard model prediction.