The word you used is considered outdated and offensive; the respectful terms are “little person” or “person with dwarfism.”

In medical contexts, dwarfism is usually defined as an adult height of about 4 feet 10 inches (147 cm) or less, caused by a genetic or medical condition. Many adults with common forms of dwarfism, such as achondroplasia, are around 4 feet (about 122 cm) tall, though there is a range and people can be somewhat shorter or closer to the 4'10" cutoff.

If you’re asking out of general curiosity, a more considerate way to phrase the question would be: “What height is considered dwarfism?” or “What height is considered a little person?”