- Go to SETTINGS >> SHIPPING RULES.
- Click the blue Add New button.
- In the field Rule Name, enter a name that describes this rule, such as "First Class Mail".
- Set the "IF" condition to Order weight is less than 15.9 oz. View all available conditions.
Order Weight | Is equal or less than | 15.9 oz
- Set the "THEN" action to Assign saved carrier selection to "First Class Mail":
Set saved carrier selection | First Class Mail
- Save your new rule and you're done!