The developments or evolution in the E&P industry, with respect to the design of drilling rigs leads to the argument “bigger is better”. The majority of newly designed rigs exhibit enormous capacities (hookload, drawworks horsepower, torque, etc.) however, the costs for these are naturally higher than for smaller rigs with lower capacities. For an efficient application of drilling rigs, a more specific description of capability limits of drilling rigs is required. A rig should not solely be chosen based on horsepower or hook load. This is not enough, especially if taking hoisting velocity in consideration, this affects the load capacity very intensively. In the course of this work, a detailed summary of nearly all worldwide rigs, currently in use, has been created. Only a fifth represents rigs with a capacity of 200 tons of HL or less. Nowadays, the trajectories of the newly planned wells are so complex that the limitation factor isn’t hookload (HL) or horsepower (HP) anymore; in horizontal wells, limitations are either based on torque or hydraulics. That’s why rigs with more HL are not always the best decision to overcome a limitation problem; for example in horizontal wells, a top drive with more torque capacity is enough to increase the possible length of the planned well path. This thesis aims of establishing a new classification system for rigs via a tool (Drilling Envelope Designer “DED”), which shows which type of operation is possible with a rig, possible areas of applications and possible limiting factors. The new classification system for rigs is derived from the classification method from the IADC bit coding system. The code consists of four character numbers: 1.True Vertical Depth (TVD)[m/1000] 2.Departure [m/1000] 3.Drill Pipe Size (DP case) 4.Kick of Point (KOP) With those four numbers, the drilling envelope borders or the scope of the selected rig are determined. The first number defines the maximum achievable true vertical depth, which stands for a vertical well, where the HL capacity is the limitation factor. The second number defines the maximum reachable departure or displacement, where torque limitation occurs. The third number provides information on the case, with which drill pipe / casing the drilling envelope was created for improved understanding and comparison with other rigs. The fourth number contributes informations on well trajectory, at which point the kick off starts. The DED in the actual version creates the DE’s on the basis of the torque and drag (T&D) formulas, which are introduced in the literature review in chapter 2. Also, details for the input parameters and information for them are mentioned in the chapter “Drilling Envelope Designer” on page 33.