Dimensions:
Small = 62 x 40 x 41 cm < 10 kg
Medium = 67.5 x 51 x 47 cm < 18 kg
Large = 81 x 56 x 59 cm < 25 kg
X-Large = 90 x 60 x 68 cm < 38 kg
XX-Large = 100 x 67 x 75 cm < 50 kg
XXX-Large = 121 x 82 x 90 cm > 50 kg
IATA Travel Guidelines - https://www.iata.org/en/programs/cargo/live-animals/pets/