Packfill: Bulk Product Weights

Find the products with no shipping weight, and fill them in bulk by product type, vendor, tag, collection or CSV. Preview every change, and undo the last batch.

See the gaps. How many of your shippable variants have a weight, and which product types are missing one.
Fill by rule. "Every T-shirt weighs 0.2 kg", applied to blanks only or to all, with a preview first.
Keep a record. Every batch is logged with old and new values, and the latest one can be undone.

Install Packfill from the Shopify App Store, then open it from Apps in your Shopify admin.