There is no mathematical formula for determining the optimum strength of the Garda Síochána, or indeed any police force. Instead, it is a matter of Government policy, taking into account all the relevant factors such as population and the crime rate, as well of course as the availability of resources.
Nor is it a straightforward matter to compare police strength in different jurisdictions. EUROSTAT, the statistical office of the European Commission, maintains statistics on police strength in the European Union, but direct comparisons using these figures are difficult to make. In order to make any proper comparison, account would have to be taken of any differences in police function. For example, the Garda Síochána is not only the national police force, but also provides the national security and intelligence service, as well as an immigration service. In other jurisdictions these functions are discharged by separate agencies.