Box size calculator: the right shipping box, in 3D

Measure the product at its widest points, then add clearance on every side for protection: about 3 mm for robust goods, 1 cm for tissue or paper wrap, 2.5 cm for bubble wrap or air pillows and 5 cm for fragile items. Product plus twice the clearance is the inside size you order. The outside is bigger by the board: about two board thicknesses on length and width, and four on height.

Box makers quote inside dimensions, length × width × height, where length is the longer side of the opening and height is the depth. That is the space your product has. Carriers measure the outside, which adds the board: a B-flute box (about 3 mm) is roughly 6 mm longer and wider and 12 mm taller on the outside, because the flaps fold in two layers top and bottom.

Multiply the outside length, width and height in centimetres and divide by 5000, the divisor most European parcel and express carriers use; some economy and air services divide by 6000. The carrier bills the higher of the volumetric and the actual weight. A 40 × 30 × 20 cm box counts as 4.8 kg even if it weighs 1.2 kg. Many domestic services price by weight and size band instead, so check your contract.

Article 24 of the EU Packaging and Packaging Waste Regulation (EU) 2025/40 caps the empty space in e-commerce, transport and grouped packaging at 50%. It applies from 1 January 2030, or three years after the Commission's implementing act on how to calculate it, whichever is later; that act is due by 12 February 2028. Filling material such as paper, air cushions, bubble wrap and foam counts as empty space. The obligation falls on whoever fills the packaging, which is often the fulfilment centre.

The calculator takes the inside volume of the box, subtracts the volume of the products (or their retail packs) and divides by the inside volume. A product of 1.2 litres in a 2 litre box leaves 40% empty space. The Commission will publish the official method by 12 February 2028, so until then treat the figure as a planning check.

E-flute (about 1.5 mm) suits mailer boxes and light retail packs. B-flute (about 3 mm) is the everyday single-wall e-commerce box, typically up to about 15 kg. C-flute (about 4 mm) cushions and stacks better. Double wall, EB or BC, is for heavy or fragile goods and boxes that will be stacked on pallets. These are rules of thumb; your box maker sets the grade from the weight and how the boxes will be stacked.

PostNL's letterbox parcel (brievenbuspakje) takes up to 38 × 26.5 × 3.2 cm and 2 kg. DHL's Kleinpaket for business customers in Germany takes up to 35.3 × 25 × 8 cm and 1 kg. InPost parcel lockers in Poland take size A up to 8 × 38 × 64 cm, B up to 19 × 38 × 64 cm and C up to 41 × 38 × 64 cm, all up to 25 kg. The calculator checks the outside size against each of them.

An EPAL Euro pallet is 120 × 80 cm, 14.4 cm high, weighs about 25 kg and has a safe working load of 1,500 kg. The calculator fills each layer with the most boxes it can, mixing two orientations where that helps, stacks layers up to the height you choose and stops at the safe load. Fulfilment centres set their own maximum height for inbound pallets, so check theirs.

Enter how many go in the box. The calculator tries every grid and every way of turning the product and keeps the arrangement with the smallest outside box, which is also the lowest volumetric weight. Untick Keep upright if the products can lie on their side: that often finds a smaller box.

Use it as the brief. The inside dimensions and board are what a box maker asks for, and Copy spec puts them in one block of text. The blank size, box weight and outside size are estimates from nominal board thickness, so ask for a sample before a large order.