Price per unit is a Shopify feature that is currently only available for merchants located in France or Germany.
To learn more about the Price per unit feature, click below to read Shopify's help guides, for Germany and France.
The following elements must be enabled/set for the price to show:
A store location set somewhere in France or Germany.
Show unit price for this product is enabled for the product within Products.
A price and measurement have been assigned, in the same space as the above.
The product has no variants enabled - you may wish to offer a product with different variants as separated products, to ensure this all appears correctly.