Antras is located some 25 km south-east of Saint-Gaudens, 20 km north-east of Bagneres-de-Luchon, and only 1 km from the Spanish border. It was part of the former province of Couserans in the Biros Valley. No district roads or highways pass through the commune and the only access to the village is by a mountain road (the Route d'Antras) from the D4 road at Sentein. There are few roads in the commune with some mountain tracks and unformed roads. The commune is mountainous and heavily forested.
The Ruisseau d'Antras flows from the commune down to Sentein where it joins the Lez which continues to Saint-Girons where it joins the Salat river.
In 2010, the commune had 62 inhabitants. The evolution of the number of inhabitants is known through the population censuses conducted in the town since 1793. From the 21st century, a census of municipalities with fewer than 10,000 inhabitants is held every five years, unlike larger towns that have a sample survey every year.[Note 1]
^At the beginning of the 21st century, the methods of identification have been modified by law No. 2002-276 of 27 February 2002 , the so-called "law of local democracy" and in particular Title V "census operations" which allow, after a transitional period running from 2004 to 2008, the annual publication of the legal population of the different French administrative districts. For municipalities with a population greater than 10,000 inhabitants, a sample survey is conducted annually, the entire territory of these municipalities is taken into account at the end of the period of five years. The first "legal population" after 1999 under this new law came into force in 1 January 2009 and was based on the census of 2006.