Pre-opened plastic bags are available in a variety of sizes and specifications, and the appropriate size can be selected based on specific uses and needs. Here are some common pre-opened plastic bag sizes and specifications:

Small bags: usually used for packaging and storage of small items, such as stationery, jewelry, pharmaceutical samples, etc. Common sizes are as follows:
Width: 5 cm - 15 cm
Height: 8 cm - 20 cm
Medium bags: usually suitable for packaging larger items, such as small gifts, clothing, cosmetics, etc. Common sizes are as follows:
Width: 15 cm - 30 cm
Height: 20 cm - 40 cm
Large bags: suitable for packaging and storage of large items, such as shoes, household items, groceries, etc. Common sizes are as follows:

Width: 30 cm - 60 cm
Height: 40 cm - 80 cm