Culverts should safely convey storm water runoff through a roadway or railway system. Due to the possibility of flow obstruction by different obstacles, culverts are mostly designed to ensure free access of air at the inlet and outlet. The above-mentioned recommendation is included in the Polish existing regulations, published by the Minister of Transport and Maritime Affairs in 2000 [Rozporządzenie... 2000]. Hydraulic design of circular culverts according to FHWA (Federal Highway Administration) and USGS (United States Geological Survey) guidelines include more types of culvert flow in a hydraulic calculations, compared to polish regulations. In this article basic rules on the most popular unsubmerged inlet circular culverts design were presented. Culvert conveyance for different types of culvert entrance according to FHWA and USGS guidelines were also compared with polish regulations and experimental data. Results show that, using a polish regulations, the calculated discharge of culvert is slightly smaller in relation to FHWA and USGS formulas.