Using the RR Lyrae surveys Gaia DR3 Specific Objects Study, PanSTARRS1 and ASAS-SN-II, we determine the Milky Way’s thick disc scale length and scale height as well as the radial scale length of the galaxy’s inner halo. We use a Bayesian approach to estimate these values using two independent techniques: Markov chain Monte Carlo sampling, and importance nested sampling. We consider two vertical density profiles for the thick disc. In the exponential model, the scale length of the thick disc is (Formula presented.) kpc, and its scale height is (Formula presented.) kpc. In the squared hyperbolic secant profile (Formula presented.), those values are correspondingly (Formula presented.) kpc and (Formula presented.) kpc. The density distribution of the inner halo can be described as a power law function with the exponent (Formula presented.) and flattening (Formula presented.). We also estimate the halo to disc concentration ratio as (Formula presented.) for the exponential disc and (Formula presented.) for the (Formula presented.) disc. © 2025 Elsevier B.V., All rights reserved.