My courier invoice shows a slightly higher weight than the calculator gave me: is the calculator wrong?
Usually not. The calculator gives the weight to two decimals with no rounding at all, while a courier may round dimensions up to a whole centimetre and push the chargeable weight up to the next half or whole kilo, with rules that vary from one courier to the next. They may also measure the packed box larger than you recorded it.
Three reasons for the gap
- Dimension rounding: a 33.5 cm side may be recorded as 34 cm.
- Weight rounding: the chargeable weight may be pushed to the next half or whole kilo, depending on the courier's rules.
- The measurement itself: a bulging carton, extra tape or a raised label adds a centimetre here and there.
The gap in numbers
A carton you measured carefully at 33.5 × 24.2 × 18.7 cm, weighing 2.1 kg, with 5000 as an example divisor. The calculator gives:
- With your exact measurements: volumetric weight 3.03 kg, which is the chargeable weight.
- If the courier rounds each side up to the next centimetre, 34 × 25 × 19 cm: 3.23 kg.
- And if the courier's rule were, hypothetically, to round the weight up to the next half kilo, the invoice would show 3.5 kg.
That is how 3.03 becomes 3.5 without anyone making a mistake. The calculator is right for what you entered, and the invoice is right under the courier's rules. The tool says as much in a fixed note under every result: carrier rounding rules are not applied.
Reconciling the invoice yourself
- Find two rules in your courier's terms: how it rounds dimensions, and how it rounds chargeable weight.
- Re-enter the dimensions in the Volumetric shipping-weight calculator, rounded the way the courier does it.
- Apply the weight rounding rule to the result by hand.
- Compare with the invoice. If the gap is still large, ask the courier for the dimensions it recorded for your parcel.
When the gap is worth disputing
When it is bigger than rounding can explain. If you worked out 3 kg and the invoice says 6, the cause is more likely a different divisor from the one you assumed, a different service from the one you chose, or a measurement recorded wrongly. A photo of the carton next to a tape measure, taken before dispatch, helps here.
So rounding does not eat your margin, add a small allowance on top of your shipping cost when you price, and work out the selling price with the Selling-price calculator.
Common questions
Why does the tool not round like couriers do?
Each courier has a different rule, and applying one would make the figure wrong for the others. The tool gives the raw figure and leaves the rounding to you.
Should I always round dimensions before entering them?
Only if your courier does and you want to match its invoice.
How many decimals does the tool show?
Two, rounding halves up.