Hi Len,

For sending a 20kg package via China Post Sea Mail (Surface Mail) to Australia, the maximum size limits are as follows:

Maximum Dimensions:
Length + Girth ≤ 3 meters (300 cm)

Girth = (Width + Height) × 2

Example: If your box is 80 cm (L) × 60 cm (W) × 50 cm (H), the girth is (60 + 50) × 2 = 220 cm. Total: 80 + 220 = 300 cm (within limit).

Weight Limit:
Max 30 kg per package (but since you're sending 20 kg, it's acceptable).

Additional Notes:
No single side should exceed 1.5 meters (150 cm).

Oversized packages may incur extra fees or be rejected.