Shopify does not have PIM or Warehouse management features like that for inventory dispensing/separation/pooling etc terms.
You could always just manage this through inventory imports using csv/excel with formula’s.
So if you know it’s always 50g units from 1kg,3kg,5kg that’s a pretty easy split and adjustments system to work out. https://help.shopify.com/en/manual/products/inventory/getting-started-with-inventory/inventory-csv
Otherwise to automate you would either need to dig through all the sku/inventory sync apps to see if there’s one that can break apart a sku by weight.
Or use a generalized automation app like usemechanic to script a custom inventory scenario.
The have some scripts to work through but this is a specific scenario you’d have to build
https://tasks.mechanic.dev/?q=sku
If you need process built you can contact me directly for services.
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Also as you have probably realized shopify is not setup for selling products by arbitrary weight.
So currently you will always have to sell in specific increments represented by a variant option (i.e. 50g,100g,etc) and quantity ordered; unless you use apps or workarounds both of which are less than ideal.
Companies in germany or france have access to a price-per-unit display system.
Good Hunting.