Ratio is a country located in eastern Osea. It is bordered by Sapin to the west, Ustio to the northwest, Recta to the north, Wielvakia to the northeast, and the Spring Sea to the southeast. Ratio's capital, Centrum, lies in the center of the country.
In December 1991, Ratio assumed control of a large portion of land in eastern Ustio, which had recently seceded from the Belkan Federation. When Belka invaded its neighbors in March 1995, Ratio was not targeted; its involvement, if any, during the Belkan War is unknown.
Ratio is located just north of the equator, which passes through the southernmost part of the country. Minor lakes are also present in the country's southeast.
- Centrum is Polish for center, referencing Centrum's position in the center of Ratio.
- Cutscene 02, Ace Combat Zero: The Belkan War.