Selling loose and by weight in an online store: sacks, variable weight and price per kilo

In a physical shop, loose goods are simple: they are weighed in front of the customer and charged at what the scales show. In an online store, the customer pays before anyone weighs anything. That is why selling by weight online requires deciding in advance exactly what you will supply and how you will charge for it.

Three different situations

• Fixed-weight packs. 250 g bags of coffee, 25 kg sacks of cement, 5 kg boxes of screws. A sealed unit with a known weight is sold. It is the simplest case, but the customer still thinks in kilos: “I need 430 kg of mortar”.
• Weighing in steps. Nuts in 100 g steps, freshly ground coffee in 250 g steps. It is weighed in the warehouse, but the customer chooses between set quantities.
• Truly variable weight. A piece of cheese, a cut of meat, a plank. The exact weight is not known until it is prepared. It is the most delicate case in an online store.

How to calculate the quantity the customer asks for

1. The customer types in the weight they need (in kg, g, tonnes or pounds).
2. Wastage is added if it makes sense: for building materials, for losses when mixing or transporting.
3. It is divided by the weight of one sales unit.
4. It is rounded up: a sack is not sold by halves.

Variable weight: three ways to keep it honest

When the real weight is not known until the order is prepared, there are three common options:

1. Selling in fixed ranges (“piece from 0.9 to 1.1 kg”) at a fixed price. Simple, but you have to absorb the difference.
2. Charging the maximum weight and refunding the difference when preparing. It requires a partial refund on every order and a good explanation before payment.
3. Authorising the payment and capturing the real amount after weighing. It depends on your payment gateway allowing it and on the customer understanding that the final charge may vary.

Whichever you choose, the customer has to know before paying. Complaints about loose goods are almost never about the price; they are about the surprise.

Price per kilo: mandatory in many cases

If you sell to consumers, Spain's price indication rules (Royal Decree 3423/2000) require, for many products, the price per unit of measure —per kilo or per litre— to be shown in addition to the selling price, and for loose products the price is precisely per unit of measure. In practice:

• The product price in the store is that of one sales unit (bag, sack, weighing step).
• Next to it the price per kilo is shown, calculated, not typed in by hand.
• In the cart and on the invoice it must be possible to see what weight was bought.

Stock by the kilo

If you sell sealed sacks, stock is in sacks. If you sell loose from a silo or hopper, the real stock is in kilos, and the store has to deduct kilos. Otherwise, you sell 40 bags of 250 g of a coffee of which only 6 kg are left.

• Decide per product whether stock is counted in units or by weight.
• For loose goods, check physical stock more often: real handling losses do exist.
• If a product has an expiry date, stock by the kilo is not enough: you also need batch and date control.

Volume instead of weight

Some products are thought of in volume: concrete and aggregates in m³, diesel or oil in litres, firewood by the stere. The logic is identical (the customer types in the volume, the store calculates whole units), but the unit changes. Do not mix them: if the customer thinks in cubic metres, do not force them to convert to kilos.

Mistakes that generate complaints

1. Not showing the price per kilo, or showing it miscalculated.
2. Variable weight without explaining how the difference is charged.
3. Shipping calculated with the wrong weight: if the store does not know that 18 sacks are 450 kg, the carrier certainly will.
4. Selling in grams what the warehouse counts in kilos (or vice versa) and rounding unintentionally.
5. Stock in units for a product that comes out of a silo.

Checklist

• Format: fixed pack, weighing in steps or variable weight.
• Weight per sales unit and product weight for shipping.
• Unit price and price per kilo visible.
• Variable weight policy written on the product page and in the terms.
• Stock in the correct unit.
• Minimums and maximums, if any.

Frequently asked questions

Can I sell the same coffee in 250 g, 500 g and 1 kg? Yes, and it is usually the clearest option: combinations of the same product, each with its own weight and price, and the price per kilo visible on all of them. The customer compares at a glance and discovers that the large format works out better.

How do I calculate shipping? With the real weight of what leaves the warehouse, packaging included. If you sell 18 sacks of 25 kg, the order weighs at least 450 kg and probably needs palletised freight, not parcel delivery. Define which carriers accept orders above a certain weight, and make sure the store does not offer options that cannot be fulfilled.

What about packaging if I sell loose food? Loose products that are packed for shipping are no longer sold “loose” as far as the customer is concerned: they arrive packed. The labelling information that must accompany them depends on the product, and food has its own rules. Check what applies to you before you start selling online what you used to serve over the counter.

And expiry dates? For food, stock by the kilo is not enough: you need to know which batch goes out in each order and which expires first. Sell first what expires first, and do not publish more stock than you can supply with enough shelf life for the customer.

How to handle it in PrestaShop

RKR Weight Pricing Pro adds a calculator to the product page where the customer types in the weight (in mg, g, kg, tonnes, pounds or ounces; you choose the store's unit and can change it per product) and sees how many sales units that is, the total weight they will receive and the price. There are four ways of selling: sacks or bags, pieces, packs of pieces and weighing in whole steps. It adds the wastage you set (default and per product), rounds up by default, supports minimums and maximums and controls stock by the kilo. The product price is still that of one sales unit and, if you wish, the price per unit of weight is also shown; units and weight travel to the cart, the order, the PDF invoice and the emails.

If what you sell is measured in volume, RKR Volume Pricing Pro does the same with m³ and litres: sacks and big bags, pieces or packs, with stock by volume.