Volumetric weight (also called dimensional or "dim" weight) is a pricing method couriers use to charge for the space a parcel takes up, not just how heavy it is. Most carriers work out both the actual weight and the volumetric weight of your box, then bill you for whichever is greater. That means an oversized box filled with lightweight goods can cost more to post than a smaller, better-fitted one, so choosing the right box size is one of the simplest ways to cut your shipping bill.
What is volumetric weight?
Volumetric weight estimates how much room a parcel occupies in a van or aircraft. Because delivery vehicles fill up with bulky, light parcels long before they reach their weight limit, couriers convert a box's dimensions into a "weight equivalent" so they can price by space. A large box stuffed with cushions or crisps weighs almost nothing on the scales, yet it still takes up a paid-for slot in the vehicle.
The idea matters most for online sellers shipping light but bulky items, such as homeware, apparel, or anything cushioned with void fill and protective padding. Get the box size wrong and you end up paying to post air.
How to calculate volumetric weight
The standard formula multiplies the three outer dimensions of your parcel in centimetres, then divides by a fixed number set by the courier:
Length (cm) x Width (cm) x Height (cm) ÷ divisor = volumetric weight in kg
The divisor varies between carriers, so it always pays to check your own courier's terms. As a general guide:
- 5,000 - used by many major couriers including DPD, DHL, UPS and FedEx when dimensions are measured in centimetres.
- 4,000 - some carriers, such as Evri, apply a lower divisor to certain services, which produces a higher volumetric figure.
- 6,000 - the IATA divisor commonly used for international air freight.
As a worked example, a box measuring 40 x 30 x 20 cm has a volume of 24,000 cubic centimetres. Divided by 5,000, that gives a volumetric weight of 4.8 kg. If the goods inside actually weigh only 2 kg, the courier will charge you as though the parcel weighs 4.8 kg, because that is the higher of the two figures.
Why couriers charge for space, not just weight
A delivery van has a fixed amount of load space and a fixed weight limit, and for most parcel networks the space runs out first. If every parcel were priced purely on weight, a courier could fill an entire vehicle with big, feather-light boxes and barely cover the cost of the trip. Volumetric weight corrects for this by making bulky parcels pay their fair share of the vehicle. In practice, carriers compare the actual scale weight with the volumetric weight and apply the higher of the two, which they often call the "chargeable weight". Understanding that single rule is the key to keeping your shipping costs under control.
Does Royal Mail use volumetric weight?
For standard domestic UK deliveries, Royal Mail does not apply volumetric weight. Instead it prices parcels by size band and actual weight. A small parcel must stay within 45 x 35 x 16 cm and 2 kg, while a medium parcel can go up to 61 x 46 x 46 cm and 20 kg. Slip over any single dimension, even by a few millimetres, and the parcel jumps into a pricier band. Volumetric weight generally only enters the picture on Royal Mail's international air services, where an IATA-style divisor of 6,000 may apply. You can always confirm the current limits on the Royal Mail website.
How the right box size saves you money
Whether your courier charges by volumetric weight or by size band, the lesson is the same: a box that fits your product snugly almost always costs less to send. Here is how to keep your parcels lean:
- Match the box to the product. Order boxes in sizes close to your actual items rather than a single one-size-fits-all option. Our small parcel boxes and e-commerce boxes come in a range of stock sizes to suit different products.
- Reduce empty space. The less air you ship, the lower your volumetric weight, and right-sizing usually means less void fill and better protection too.
- Mind the depth. Height is often the dimension that tips a parcel into the next size band, so keep boxes as shallow as your product allows.
- Choose the right board. A well-chosen corrugated grade protects goods without adding needless bulk or weight.
- Weigh and measure before you commit. Check both the actual and volumetric figures on a sample parcel so there are no surprises at the checkout.
Frequently asked questions
What is volumetric weight in simple terms?
It is a way for couriers to charge for how much space a parcel takes up rather than only how heavy it is. If your box is large but light, the courier may still bill you as though it were heavier, because it is occupying more room in the vehicle.
How do I calculate the volumetric weight of a box?
Multiply the length, width and height of the box in centimetres, then divide by your courier's divisor, which is often 5,000. The result is the volumetric weight in kilograms. Compare it with the actual weight and expect to be charged for whichever is higher.
Does Royal Mail charge by volumetric weight?
Not for standard UK domestic parcels. Royal Mail prices those by size band and actual weight. Volumetric weight generally only applies to some of its international air services, where a divisor of 6,000 may be used.
Why does a bigger box cost more even when it is not heavier?
Because delivery vehicles run out of space before they run out of weight capacity. A bulky, light parcel takes up room that could otherwise carry other items, so couriers price it by volume to reflect that.
How can I lower my volumetric weight?
Use the smallest box that safely fits your product, keep the depth as shallow as possible, and minimise empty space with efficient packing. Right-sizing your boxes is the most reliable way to bring the figure down.
Get the right size box for every order
Shipping smarter starts with better-fitted packaging. At Fast Printed Boxes we print your branding onto a wide range of stock box sizes, so you can match the box to the product and keep both your volumetric weight and your postage costs down. Browse our full range of custom printed boxes to find the right fit for your orders.