Volumetric weight calculator

What is volumetric weight?

Volumetric weight is a second weight worked out from a parcel’s measurements rather than its mass. A carrier sells space in a van, not weight on a scale: a duvet weighs almost nothing and fills a shelf, a box of books is the opposite. So every carrier works out what the parcel costs in space, and charges on whichever of the two figures is greater.

It is the reason a light parcel can come back dearer than expected, and the single most common surprise on a courier quote.

How do I calculate volumetric weight?

Length × width × height in centimetres, divided by 5,000. Every courier service compared on this site uses that divisor, so the same box gives the same volumetric weight whoever carries it.

Which divisor does An Post use?

An Post divides by 6,000, not 5,000. It is stated on their own sending guide and almost nowhere else, and it means the same box gives two different answers depending on who is carrying it. The An Post figure is always the lower of the two.

Worked on a 60 × 40 × 30 cm box, 72,000 cm³. An Post’s divisor and their own worked example, a 62 × 49 × 39 cm item at 19.75 kg, rounded up to 20 kg, are published on anpost.com and were read 14 August 2026.

The calculator above applies the courier divisor of 5,000, because that is what every price on this site is quoted under. If you are posting over the counter instead, use the An Post row: that box is 12.0 kg to them, rounded up to 12 kg, and An Post stops carrying parcels above 20 kg at all.

What is chargeable weight?

The greater of the volumetric weight and the weight on the scales, rounded up to the next band the carrier prices in. It is the only number that decides the price, and it is what the calculator above returns.

Two parcels can weigh the same on the scales and cost different amounts, and two parcels can be the same size and cost different amounts. Chargeable weight is what reconciles that, and once you have it you can compare carriers on a single number.

Which weight band does it price at?

Carriers price in steps rather than by the gram, and a chargeable weight is always rounded up into the next step. A 2.4 kg parcel prices at the 3 kg band, here and at the booking page.

Cheapest price we hold for a parcel sent within Ireland at each band, from our weekly market check, run Friday, 14 August. Prices to other destinations are on the destination pages.

Measuring the box

Measure the outside of the box once it is taped shut and packed, not the thing going inside it. Round each side up to the next centimetre, and include any bulge: the depot measures what arrives, and a parcel that measures over gets re-rated at the higher band after collection.

Weigh it packed too. Tape, filler and the box itself are part of the weight, and an item that weighs 940 g on its own can leave the house at 1.05 kg, which pays the 2 kg price.

Getting the number down

A smaller box is the whole trick. Taking that 60 × 40 × 30 down to 50 × 35 × 25 drops the volumetric weight from 14.4 kg to 8.75 kg, which moves it from the 15 kg band to the 10 kg band. Fill dead space with soft padding rather than stepping up a box size, and split a big light load into two small parcels if the sum says it is cheaper.

Common questions

Once you know the chargeable weight, compare what the carriers charge for it, or read the size and weight limits guide for what fits in each band.