Bang Krathum's topography consists of flat, fertile lowlands.

Clockwise from the north, the subdistrict is bordered by Wang Nam Khu (of Mueang Phitsanulok District), Tha Tan, Nakhon Pa Mak, Phai Lom, Ta Fo (of Mueang Phichit District in Phichit Province), Sanam Khli, Khok Salut and Ban Rai.

Bang Krathum lies in the Nan Basin, which is part of the Chao Phraya Watershed.

The town of Ban Bang Krathum is on the tambon's chief watercourse, a canal which winds through farms heading north-east to Ban Bang Kranoi in Nakhon Pa Mak, where it joins the Wang Thong River.

The subdistrict is divided into 11 smaller divisions called (muban), which roughly correspond to the six villages in Bang Krathum.