How to base Free Shipping on weight
Step 1: Login to the admin panel.
Step 2: Using the top menu bar, hover over the Shipping tab and select the Shipping option.
Step 3: This brings you to the Shipping configuration screen. Look for the field named Free shipping starts at that has the lb to the right side of the data box.
Step 4: You may have a different weight if your default is set differently. Enter the total weight you wish to set the free shipping to. For example, we set Free Shipping to begin when the total order weighs 10 pounds.
Step 5: Click on the green Save button located in the upper right corner of the screen.