Note: All these size recommendations are only applicable to hairless cats. The XS size is suitable for new born baby weighing 1-2 pounds (approximately 0.5-1 kg).suit for bellow 2 months. The S size is suitable for babies weighing 2-3 pounds (approximately 1-1.5 kg). Suit for 3-4 months. The M size is suitable for babies weighing 4-5.5 pounds (approximately 2-2.7 kg). suit for 5-6 months. Size L is suitable for 5.5-7 pounds (approximately 2.7-3.5 kg). suit for 7-8 months. The XL size fits 7 – 9 pounds (approximately 3.5-4.5 kg). suit for 9-11 months. The XXL size fits 10-12 pounds (approximately 5.0-6 kg). suit for Adult. If your cat is not hairless, but like our shirt, please order one size larger. For more size information, please refer to the size chart below.