Grocery, bulk or refill product
Show the price per unit next to the pack price.
Each example below is the actual published output of the Unit price widget for sample WooCommerce products. The unit price is the product's current price divided by the pack quantity, formatted in the shop currency (GBP, prices shown excluding tax).
A sample 250 g coffee priced £6.00 whose ACF Number field holds 2.5 (units of 100 g): £6.00 ÷ 2.5 = £2.40 per 100 g.