The ability of an ant to survive a fall largely depends on its size and the surface it lands on. Generally, smaller ants are more likely to survive a fall than larger ones, and landing on a softer surface can also increase their chances of survival.
However, to give you a rough estimate, it's been suggested that ants can survive falls from a height of around 1.5 to 2 times their body length, which is usually between 0.08 to 1 inch depending on the species. So, for instance, a 0.5 inch long ant may be able to survive a fall from a height of up to 1 inch or so.
It's worth noting that even if an ant does survive a fall, it could still be injured or stunned, so it's best to avoid dropping ants or other insects from heights whenever possible.