Your sentence is almost correct, but it can be improved slightly for clarity and grammar. Here is a better way to say it:
A karate uniform consists of a jacket and pants (together called a gi) and a belt.
Explanation:
- Adding “a” before gi is necessary, because “gi” is a singular noun and should be preceded by an article.
- The rest of the sentence is clear and correct.
So the corrected sentence is: A karate uniform consists of a jacket and pants (together called a gi) and a belt.