Area of the province which is surrounded by Bozdağ and Sündiken Mountains at North, Emirdağ at South, Orta Asya Valley at East, Türkmen Mountain at West, is about 13653 km2. That much of area covers 1.8% of Turkey. Elevation of the city center from sea is 792m.

Eskişehir province is surrounded by Emirdağ and İnsaniye counties of Afyonkarahisar at South, Yunak county of Konya at Southeast, Polatlı, Nallıhan and Beypazarı counties of Ankara at East, Göyük county of Bolu at Northwest, Gölpazarı, Söğüt, Bozüyük counties of Bilecik and Kütahya province at West.

About 22% of the province area is composed of mountains while plains have %26 share of the area.

Topographical structure of Eskişehir province which is Northwest corner of Interior Anatolia, is consists of plains in Sakarya and Porsuk river basins and mountains surrounding those plains. Bozdağ-Sündiken mountain chain from North, Türkmen Mountain located at the east corner of Interior West Anatolian threshold, Yazılıkaya Plateau and Emirdağ from West and South, surround plains of river basins.

The valleys generally became deep as a result of wearing of outer factors for a long time. Shoulders of valleys have a little inclination and wearing of shoulder is strong. Top of the hills are pressed and round except new formations in the province where closed basin situation is not observed. There is continuous slope towards to sea.

Mountains surround plains of province from different sides. The shapes that are formed as a result of different kinds of wearing and dissolution are generally clear in mountainous areas. There are plateaus lying from plains to mountains in different elevations. There are Bozdağ and Sündiken Mountains that are Interior Anatolian mountain chains at North of the province on the direction of west-east and the extensions goes to Sakarya river that constitutes province border.

Sivhisar Mountains which begin inside the arc of Sakarya, at Southeast corner of Eskişehir province, lies in the direction of Southeast-Northwest direction. Sivrihisar Mountains lying towards Kaymaz sub district is located on a plateau which has a threshold appearance.

After passing Kaymaz sub district, high hills are observed on the wide threshold which has a plain appearance. That structure of wavy area with plain like appearance continues to West.That structure forms Türkmen Mountains at the South of Sarısu Plain and unites with Domaniç Mountains outside the borders of province. The most important altitude between Kaymaz sub district and Eskişehir city center is the foot of Koca Kır Plateau going down to Porsuk Plain. While going to West from Porsuk Creek, one reaches to Küçük Türkmen Mountain at 1255m height. At far more West there are Kozdoğru and Göktepe hills.