You can change the weight type for your products by following the simple steps below.
Step 1: Open Simple Invoice from your Shopify store’s “Apps” section.
Step 2: Click on the “Templates” on the Simple Invoice dashboard.
Step 3: Click on the Formats section, click on the Weight Type option, and select the type you wish to print in your invoices from the dropdown menu.
Step 4: Click on the Save button.