Arghakhanchi lies between 27'45"N and 28'6"N latitude, and 80'45"E to 83'23"E longitude. It covers 1,193 km². 68% of the district is in the mountainous Mahabharat Range and the rest is in the Siwalik Hills. Elevations range from 305–2575 m above sea level and about 40% of the total area is forested.
Arghakanchi is surrounded by Lumbini Zones Palpa district to the east, Gulmi to the north, and by Terai districts Kapilvastu and Rupandehi to the south. To the west are Rapti Zones Pyuthan and Dang districts.
The extreme western part of the district borders Jhimru Khola a tributary of the Rapti. Otherwise the Mahabharat Range is the main hydrographic boundary where northern slopes drain into the Kaligandaki River and everything south of the crest drains into minor drainages ultimately crossing into Uttar Pradesh, India. Streams in the district include Bangikhola, Bangsari Khola, Mathurabesi Khola, Banganga Khola, Durgakhola, Sitakhola, Khakabesi Khola, Rangsing Khola, Ratne Khola, Jhimruk Khola and Khankbesi Khola etc. Lakes in the district are Thada lake and Sengleng lake.