Arnum is an urban Settlement in Haderslev Municipality, in the region of Southern Denmark, Denmark. Arnum lies at 28 m above sea level. It has 481 inhabitants (2026). The nearest city is Haderslev, 33 km to the east. Among the landmarks around are Ribe Cathedral (15.9 km), Riberhus (16.3 km) and Ribe Kunstmuseum (15.6 km).