Abstract The exact origins of many Type Ia supernovae—progenitor scenarios and explosive mechanisms—remain uncertain. In this work, we analyze the global Suzaku X-ray spectrum of Kepler’s supernova remnant (SNR) in order to constrain the mass ratios of various ejecta species synthesized during explosion. Critically, we account for the Suzaku telescope effective-area calibration uncertainties of 5%–20% by generating 100 mock effective-area curves and using Markov Chain Monte Carlo–based spectral fitting to produce 100 sets of best-fit parameter values. Additionally, we characterize the uncertainties from assumptions made about the emitting volumes of each model plasma component and find that these uncertainties can be the dominant source of error. We then compare our calculated mass ratios to previous observational studies of Kepler’s SNR and to the predictions of Type Ia simulations. Our mass ratio estimates require a 90% attenuated 12 C+ 16 O reaction rate and are potentially consistent with both near- and sub- M Ch progenitors, but are inconsistent with the dynamically stable double-detonation origin scenario and only marginally consistent with the dynamically unstable dynamically driven double-degenerate double-detonation (D 6 ) scenario.