Trivia: Producers Gale Anne Hurd and Sam Mercer wanted to film the movie at the American Museum of Natural History in New York. However, the museum's administration was afraid that the film would not only cast the museum in an unflattering light, but it would also scare kids away from the museum. They were given permission by the Field Museum of Natural History in Chicago to film there, because they loved the movie's premise.
Trivia: The Kathoga has only five minutes of screen time in the entire film.
Answer: While the size is never explicitly stated, the creature does seem to be somewhat larger than a tiger and approaching the size of a horse when the scene needs it to be. Perhaps its size changes as it eats and needs sustenance?
Erik M.