If you can obtain an Operators Manual for that make and model, it should have that info in the contents. It did for my Kubota L4400. Two other options are calling your nearest Kubota Dealer, or a large Tire Service Shop in your area. Hopefully a TBN member that owns that Model will chime in, BTW, Welcome aboard. Best wishes.
Thats an elusive machine, nothing found on the Internet. Give us the Front and Rear tire size plus type (R4, AG, Turf, Rice )and maybe a picture of your tractor.