Guide · Updated 2026-10-08

Volumetric Weight Explained: Choose the Right Box

Why couriers charge for box size as well as weight, how to calculate volumetric weight with the usual divisors, and how to pick the smallest box that saves postage.

A light parcel in a big box can cost as much to post as a heavy one, because couriers charge for the space a parcel takes up in their vehicles. The charge is based on the larger of two figures: the parcel's actual weight and its volumetric weight.

The formula

Volumetric weight (kg) = length x width x height (all in cm) ÷ divisor. A divisor of 5,000 is common, and some carriers and services use 4,000 or 6,000 for different services. Always ask your courier which divisor they use.

Worked examples with a divisor of 5,000

In each case, the chargeable weight is the volumetric weight, because it is higher than the 1 kg actual weight. Moving from the 45 x 35 x 25 cm box to the 25 x 20 x 15 cm one (if the contents fit) cuts the chargeable weight from about 7.9 kg to 1.5 kg.

Finding the smallest box that fits

Start with the product's dimensions and add padding on every side, typically 5 to 10 mm of cushioning for sturdy items and more for fragile ones. If you are sending several items, they will often pack as a grid. Try each way of turning the item, because rotating a flat product can drop it into a much smaller box. The Shipping Box Selector tries every orientation, counts how many fit and shows both volumetric and chargeable weight.

Ways to cut shipping cost

• Use the smallest box that gives the protection you need, not the smallest that technically fits.
• Buy boxes in a few sizes that fit your best sellers, not dozens of sizes.
• Use padded envelopes or bags for soft goods that need no box.
• Compare services: a courier that uses a divisor of 6,000 charges less for bulky light parcels than one using 4,000.
• Weigh a packed parcel and measure it with its tape and padding, since the carrier measures the finished parcel.

Do not forget labels and storage

A standard shipping label is 4 x 6 inches (about 102 x 152 mm); the Label Printer Finder works out the printer width and cost per label. For storing stock before it ships, the Storage Box Fit Finder shows how many boxes fit on a shelf.

Frequently asked questions

Do all couriers use volumetric weight? Most do for at least some services, but the divisor and thresholds differ. Check your courier's terms.

Which dimension counts as length? Carriers usually use the longest side, but volumetric weight multiplies all three, so the order does not matter.

Divisors and rules vary by carrier and service and change over time. These examples show the method only.