Most of the literature on government size mainly measure it as government expenditure as a percentage of GDP. Are there other monetary of non-monetary measures of government size?
Another common measure is the rate of public service employment vs total employment. You can also use any relative measure of employees in public administration if you want to limit the scope.
1. Total number of employees in the government (public services) and semi-government (state-owned enterprises and statutory authorities/commissions/boards) institutions as a proportion of the total labour force in the country and as a proportion of the total population (i.e. number of pubic sector employees per capita).
2. Total consumption / recurrent expenditures of the government as a proportion of the total private consumption expenditures.
3. Total public (recurrent) expenditures per capita
4. Total number of Ministries and Government Departments in a country.
I would first define government, since it could include central as well as local government, where "central" should correspond to the country, while "local" might correspond to several levels, each of which (according to the principle of subsidiarity) may have duties, as well as a budget, which otherwise would belong to the central government