XS
Parameters: Back length for two wheels 22~33cm | Back length for four wheels 27~38cm | Chest circumference 36~46cm | Back height <31cm
Reference weight: 3.5–8kg (7–16 jin)
Suitable for: Small dogs (Poodle, Chihuahua, Pomeranian, small mixed breeds)

S
Parameters: Back length for two wheels 22~33cm | Back length for four wheels 27~38cm | Chest circumference 42~52cm | Back height <35cm
Reference weight: 8–14.5kg (16–29 jin)
Suitable for: Bichon Frise, Schnauzer, small Corgi, Pug, small to medium terriers

M
Parameters: Back length for two wheels 35~48cm | Back length for four wheels 40~53cm | Chest circumference 46~56cm | Back height <36cm
Reference weight: 15–24kg (30–48 jin)
Suitable for: Standard Corgi, Shiba Inu, Border Collie, medium-sized mixed breed dogs, French Bulldog

L
Parameters: Back length for two wheels 35~48cm | Back length for four wheels 40~53cm | Chest circumference 50~62cm | Back height <40cm
Reference weight: 25–36kg (50–72 jin)
Suitable for: Golden Retriever, Labrador, German Shepherd, Staffordshire Bull Terrier, medium to large domestic dogs

Additional notes
Short and stocky dogs (English Bulldog, Pug): Increase weight by 2~4kg for the same size;
Slim breeds / Greyhound types: Decrease weight by 3~6kg for the same chest circumference;
For wheelchair selection, prioritize chest circumference data, weight is only for reference.