This post is going to show you how many stars upgrade coupons you need to upgrade your turf skins. Only the upgrade requirements for the default turf, 1 Year Anniversary Turf & Frozen Winter Turf seem to be different while all the other turfs seem to have the same requirements. However, in case you find a turf with different requirements, please let me know in the comments down below so I can update this page.
1 Year Anniversary Turf:
Frozen Winter Turf: