Tonnage isn't a trophy number — it's a match between heat load and cooling capacity. Oversized units short-cycle; undersized ones never catch up on peak Hyderabad afternoons.
Start with usable area, then factor orientation, glazing, occupancy, and equipment heat. For many apartments, a quick rule of thumb is a starting point only — site surveys still win.
If you're evaluating a new install, pair the load calc with duct or piping layout early. Comfort fails when design and install don't talk.