It is crucially important to select a proper TBM and define its basic specifications such as installed cutter-head torque and TBM thrust capacities for a special job. Underestimation of these parameters would reduce excavation performance. In order to generate a general guidance on determination of some of TBM specifications, a database including 262 TBMs' design parameters is established. The statistical relationships between the design parameters of 262 TBMs (72 open, 24 single shield, 41 double shield, 86 EPB and 39 slurry TBMs) manufactured after 1985 in the world are investigated and theoretical concepts behind the relationships between TBM diameter and installed thrust capacity, nominal cutterhead torque capacity, total weight, maximum rotational speed of cutterhead, and number of disc cutters are discussed. Some of the correlations between these parameters are found to be strong. The results are summarized in a table given upper and lower limits of predicted values. At the end, some data obtained in different 30 tunnels excavated in different geological conditions with different TBMs in Turkey are discussed to test the validity of predictor equations developed within the frame of this study. (C) 2013 Elsevier Ltd. All rights reserved.