Weight discrepancies and who pays for them

You declare a weight. The courier measures the parcel at its sorting facility and charges for what it actually is. Where the two differ, the courier's figure applies and a correction appears on your invoice weeks later.

Individually these are small. Systematically they are one of the more removable costs in ecommerce fulfilment, and most stores never look at them because they arrive as unlabelled adjustments inside a large invoice.

Volumetric weight, which is where most of it comes from

The mechanic that surprises people: couriers charge on the greater of actual weight and volumetric weight.

Volumetric weight is calculated from the parcel's dimensions using the courier's own divisor, and it exists because a van fills up by volume before it fills up by mass. A large light parcel occupies space that could have carried something heavier, and the pricing reflects that.

The consequence for a store: an oversized box costs money regardless of what is inside it. A small item in a large carton is charged as though it were heavy, and the fix is packaging rather than negotiation.

This is also why declared weight alone is not enough. A system that quotes delivery on product weight and ignores dimensions will under-quote systematically on bulky items, and the difference lands as a correction every time.

Where discrepancies come from

Five causes, in rough order of how often they are responsible.

Product weights are wrong or missing. Entered once at product creation, estimated, never checked. If a product's recorded weight is under its true weight, every parcel containing it is corrected.

Packaging is not counted. The box, the filler, the tape and the documents all weigh something. A quote based on product weight alone is short by that amount on every parcel.

Dimensions are not recorded at all. So volumetric weight cannot be calculated, and any parcel where volume exceeds mass is under-quoted.

Packing varies by person. Different staff use different boxes for the same order, so the same order can be charged differently on different days.

Multi-item orders. Weights add up; the box does not necessarily match. Combining three items may need a larger carton whose volumetric weight exceeds the sum of the parts.

All five are correctable with data that is cheap to collect and rarely collected.

Finding out how much it is costing you

The exercise takes an afternoon and it is worth doing once properly.

Extract every weight correction from the last three months of courier invoices. This requires consignment notes recorded against orders, otherwise the corrections cannot be traced back to anything — see capturing the consignment note against the order.

Total them. The absolute figure is usually larger than expected, and it is a pure cost with no revenue against it.

Group by product. The distribution is almost never even. A small number of products generate most of the corrections, and those are the ones with wrong data or bad packaging.

Look at the direction. Corrections should be roughly random if your data is accurate. Consistently upward means your declared weights are systematically low, which is a data problem rather than a measurement dispute.

That last check is the important one. Random corrections are the cost of measurement tolerance. One-directional corrections are a fixable error.

Fixing it, in order of return

Weigh your top products. Not all of them — the ones that appear in most orders. An hour with a scale removes most of the problem.

Record dimensions as well as weight, so volumetric weight can be calculated before the courier calculates it for you.

Include packaging in the calculation. Either as a per-box addition or by recording the weight of each box type you use.

Standardise boxes. A defined set of carton sizes with known dimensions and weights makes quoting predictable and stops the same order being packed differently on different days.

Review the products generating corrections and adjust their data or their packaging specifically.

The return shows up in two places: the corrections stop, and your delivery quoting at checkout becomes accurate — which means you stop under-charging customers for delivery on exactly the parcels that cost most — see shipping revenue versus shipping cost.

When to dispute

Most corrections are legitimate and disputing them is not usually the best use of attention. Three cases where it is.

The corrected weight is implausible. A parcel charged at several times what its contents could possibly weigh is an error, and couriers will correct it when shown.

The same product is corrected inconsistently. Charged correctly on some parcels and corrected on others suggests a measurement or handling issue rather than a data one.

The correction applies a rate you do not have. A surcharge or band that is not in your agreement.

For any of these, having recorded your declared weight and dimensions at dispatch turns the conversation from an assertion into a comparison — which is the practical reason to store them.

Common questions

Why does a courier charge more than the declared weight?

Because it weighs and measures the parcel itself and charges on the greater of actual and volumetric weight. Volumetric weight is derived from the parcel's dimensions using the courier's divisor, so a large light parcel is charged as though it were heavy — meaning an oversized box costs money regardless of its contents.

What causes most weight discrepancies?

Product weights that were estimated at creation and never checked, packaging weight not being counted, dimensions not being recorded so volumetric weight cannot be calculated, packing that varies between staff, and multi-item orders needing a larger carton whose volumetric weight exceeds the sum of its contents.

How do you tell a data problem from measurement tolerance?

By the direction of the corrections. If your declared weights are accurate, corrections should be roughly random in both directions. Consistently upward corrections mean your recorded weights are systematically low, which is a fixable data problem rather than a dispute about measurement.

What is the highest-return fix?

Weighing the products that appear in most orders — an hour with a scale removes most of the problem — followed by recording dimensions so volumetric weight can be calculated in advance, including packaging weight, and standardising on a defined set of carton sizes so the same order is not packed differently on different days.

Related: courier invoices and how to reconcile them · shipping revenue versus shipping cost · capturing the consignment note against the order