Google Merchant GTIN for Woocommerce
Adds a custom field to the product page to add a GTIN number for your Google Merchant product feed.
You can view this field in the Inventory tab.
You can also use the Woocommerce import to import this field in bulk, just add a column to your csv called: Meta: _gtin and import as custom meta.
NOTE: Only works for a simple product NOT a variable product.