How to determine the concrete security of lattice cryptosystems?
Depending on whether your lattice-based cryptosystem has security reduction or not, there exists two types of parameters:

$\textbf{1. Provably secure:}$ For a cryptosystem with provable security, the parameters are chosen according to the underlying reduction. For example, suppose your cryptosystem is based on the hardness of LWE problem. Now, assuming that the desired security level $\ell$ is identical to the hardness level of the LWE problem (i.e., without involving the gap induced by the security reduction), one can determines the best known solver $D$ for the LWE problem and ensures that its corresponding
parameters offer a hardness of $\ell$ bits. In order to find also the best known solver for LWE and measure the bit hardness of LWE instances, the estimator by Albrecht et al. [APS15] can be used.

$\textbf{2. Non-provably secure:}$ If the cryptosystem is not provably secure, then identify the best known attack $A$ on the cryptosystem and select parameters satisfying $\frac{t_A}{\varepsilon_A} \geq 2^{\ell}$, where $t_A$ and $\varepsilon_A$
are the running time and success probability of $A$, respectively.

See this paper for more details.