Hey Growmie,
Here are some indicators when your plant is ready for a new container:
Young plants in small containers are usually ready to be transplanted after they’ve sprouted 4-5 sets of leaves (this may vary from strain to strain). Check the drainage holes at the bottom of the container—a plant should have a healthy and visibly white root system. Any discoloration or darkening may indicate that the plant has become rootbound, and a transplant should take place immediately. Many growers opt to transplant to a finishing pot in the final two weeks of vegetative growth before a plant transitions into the flowering phase. At this point, a plant will explode both in size and volume and will require a substantial amount of space for root development. Hopefully, I answered your question and remember Happy Growing and Free your mind one puff at a time.