Display omitted •Three novel low-cost optimization approaches of a commercial MW resonator for three experimental purposes (CW, transient and pulse EPR) are proposed.•The simulated enhanced B1 homogeneity could be experimentally verified by the perturbing sphere method and by CW EPR measurements on BDPA.•Application of time-resolved EPR spectroscopy on light-induced triplet states in pentacene revealed an enhanced MW conversion for all proposed resonator optimizations.•The resonator characterization by CW and pulse EPR measurements show improved volume sensitivity. Microwave (MW) resonators in Electron Paramagnetic Resonance (EPR) spectroscopy concentrate the MW magnetic field (B1) at the sample and separate the MW electric field from the sample. There are numerous experimental methods in EPR spectroscopy which all impose different requirements on MW resonators (e.g. high or low quality factor, MW conversion, and B1-field homogeneity). Although commercial spectrometers offer standardized MW resonators for a broad application range, newly emerging and highly-specialized research fields push these spectrometers to or beyond their sensitivity limits. Optimizing the MW resonator offers one direct approach to improve the sensitivity. Here we present three low-cost optimization approaches for a commercially available X-band (9–10 GHz) MW resonator for three experimental purposes (continuous-wave (CW), transient and pulse EPR). We obtain enhanced MW conversion factors for all three optimized resonators and higher quality factors for two optimized resonators. The latter is important for CW and transient EPR. Furthermore, we fabricated a resonator which features an extended area of homogeneous B1-field and, hence, improved pulse EPR performance. Our results demonstrate that small changes to a commercial MW resonator can enhance its performance in general or for specific applications.