Everything you'd want to know before you install.
A detailed look at how Unit Price per Kg & Sell by Weight PrestaShop 8 & 9 works, why we built it the way we did, and the thinking behind the features above.
A legal requirement PrestaShop leaves to the merchant
EU Directive 98/6/EC requires the price per unit of measure for products sold by weight, volume or length. France applies it through the decree of 3 December 1987, Germany through the PAngV, which also requires a price per 1 kg or 1 l in the immediate vicinity of the price. PrestaShop offers a “unit price” field typed by hand: it has to be recalculated at every price change, and it ignores discounts and group prices.
The calculation starts from the net content
You enter the net content once, on the product or on each combination: 750 g, 1.5 l, 25 m. The module divides the price shown to the customer by that content and expresses it per 1 kg or 100 g, 1 l or 100 ml, 1 m, 1 m² or 1 m³. The same product in 250 g and 1 kg shows two different prices per kilo, and a German customer always sees a price per 1 kg, even if you chose 100 g for the rest of Europe.
Sale by customer-chosen weight
The net content becomes a sale step, for example 100 g, and the product price is the price of one step. On the product page, the quantity field is replaced by quantity buttons and a +/- selector that move step by step, with the total shown live. In the cart, the quantity is the number of steps: 700 g is 7 steps. Stock is still counted in steps, since PrestaShop does not handle decimal quantities, and the back office product page shows the conversion (stock 50 = 5 kg).
Pieces at actual weight, settled after weighing
For a piece whose exact weight is only known during preparation, the customer pays the price of a piece of average weight. On the order page, a weighing panel waits for the actual weight of each line and calculates the pro rata refund. On validation, the module creates a PrestaShop credit slip, emails the weights to the customer and, if you choose so, a voucher for the difference. A piece heavier than expected costs the customer nothing extra.
Hundreds of products in a few minutes
The bulk editor in the configuration lists your products by category, with a filter on those without net content yet. Net contents written in names are detected and pre-filled, “6 x 33 cl” packs are multiplied, dimensions such as “40x60 cm” are ignored. Combinations whose name contains a net content are filled at the same time.
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