Check out this video that fully details what UTR is:
What is a UTR? Why should I have one?
UTR (Universal Tennis Rating) is a number that provides a real and accurate measurement of skill level. A player’s UTR is a number between 1.00 and 16.50.
One match result is all it takes to receive a projected UTR. After approximately five matches, the rating becomes fully reliable. As matches are played and entered into the system, a player’s UTR will increase or decrease over time to reflect their current skill level.