Tonga Business Directory: TON is the ISO 3 alphabet country code of Tonga. Currency of Tonga is T$, which has a short code of TOP. Capital of Tonga is Nuku'alofa. Tonga has the population of 109008 and approximate area is 747.00 square kilometers (or approx. 464.1858 square miles). Population density of Tonga is approx. 145/Km2 (or approx. 90.103/mile2)