Add Weight to Orders Containing Specific SKUs - Shipping Rules

In the field Rule Name, enter a name that describes the rule.

For example, “Apply Weight to SKU…“

Set the "IF" condition to Item SKU and select your logic. For example, Is Equal To will apply to all SKUs that exactly match what you are typing in, and Contains will apply to all SKUs that contain what you type in. From there, type in the SKU or partial SKU that you want this rule to apply to.

Set the "THEN" action to Add to order weight and enter in the weight of the product.