Pressure swing adsorption (PSA) process is one of the candidate processes for $CO_2$ capture. The interest has led to the development of various new adsorbents such as modified zeolite materials and metal-organic frame-works (MOFs). The developed adsorbents are evaluated through lab-scale methods based on simple indicators like working capacity and selectivity. However, these indicators do not accurately indicate and adsorbent's per-formance in a PSA process. In this work, we propose new performance indicators that better reflect the actual process-level performance: efficiency and purity. Both indicators are derived for an idealized PSA process with the extended Langmuir isotherm model, which means they serve as limits of the achievable performance of a PSA process with the tested adsorbent. For simple calculation and quick evaluation, the performance indicators are derived as explicit analytical expressions. Because the indicators are derived with the assumptions of an idealized PSA process, their calculations only require isotherm parameters rather than other process parameters, such as heat of adsorption and mass transfer coefficients, which are harder to obtain experimentally. In order to test whether an adsorbent in question can achieve target purity, the upper bound of purity is also derived by assuming an extreme operating condition. Case study involving the evaluation of zeolite 13X, activated carbon, and Cu-BTC is presented to show the use of the new performance indicators, and the results are compared with rigorous simulation results.