Without further information, it's hard to say. Autoflowering plants can range from 30cm to 120cm depending on the strain, growing method, and training technique. Autos also grow during the flowering stage... but this can vary greatly as mentioned before. It can be limited to 10-15cm, but with sativas, it can also reach up to 30cm. If it gets too tight upwards in the tent, use a net or gently tie the tops down a bit. I'm currently training my plants and using LST clips and a net. Good luck and happy smoking!