The performance of the fiscal policy is largely affected by the relationship between government size, composition of public spending and economic growth. We use a theoretical framework to find optimal relations among these variables and confront them with a panel data for the Brazilian states. Private capital and government spending are substitute inputs in production as the Brazilian states require provision of public spending to fill gaps in the underdeveloped private sector. Public investment and current government expenditures are combined in fixed ratios in the overall government spending due to strong rigidity of the public budget. The optimal share of public investment is considerably lower than current expenditures, as occurs in developing countries characterized by low economic dynamism. Finally, the average tax burden from the data is below the estimated optimal level, meaning that there is space for increasing tax rate without harming economic growth for some Brazilian states.