ANSWER: 5-6 centimeters = over 2 inches
… Ants range in size from 0.75 to 52 millimeters (0.030–2.0 in), the largest species being the fossil Titanomyrma giganteum, the queen of which was 6 centimeters (2.4 in) long with a wingspan of 15 centimeters (5.9 in) [source].
… The largest living ant in the world today is the Queen Driver Ant. Whilst the minions beneath her are just 5 millimeters in length and soldier ants are slightly bigger at 15 millimeters – the queen grows as long as 5 centimeters [source].
… The Bullet Ant can get up to 3 centimeters [source].