Volumetric Weight Calculator. Know what you're really paying for.

Volumetric weight (also called dimensional weight or DIM weight) is a carrier's estimate of how much space a parcel takes up on a van or plane, expressed as a weight. A big, light box costs the carrier as much to move as a small, heavy one, so they charge for whichever is greater: the parcel's actual weight on the scales, or its volumetric weight. That higher figure is the billable weight on your invoice.

Multiply the parcel's length, width and height in centimetres to get its volume in cubic centimetres, then divide by the carrier's divisor. DHL Express, FedEx, UPS, TNT, DPD's Air services and Evri's international service all use 5000. DPD's standard ground parcel service uses 4000, which makes the same box come out heavier. Evri prices UK parcels on weight alone. So a 40 × 30 × 20 cm box is 24,000 cm³: 4.8 kg volumetric at 5000, or 6 kg at 4000. In inches and pounds, DHL, FedEx and UPS publish a divisor of 139.

Billable weight (sometimes chargeable weight) is the figure the carrier actually prices your parcel on. It's the higher of actual weight and volumetric weight, usually rounded up to the next 0.5 kg. If your parcel weighs 2 kg but has a volumetric weight of 4.8 kg, you're billed for 5 kg. The gap between the two is what people mean by paying to ship air.

No. Royal Mail prices parcels by size band and actual weight rather than a volumetric formula. The bands are Letter (up to 24 × 16.5 × 0.5 cm and 100 g), Large Letter (up to 35.3 × 25 × 2.5 cm and 750 g), Small Parcel (up to 45 × 35 × 16 cm and 2 kg) and Medium Parcel (up to 61 × 46 × 46 cm and 20 kg). Anything bigger or heavier needs Parcelforce or a courier, and volumetric pricing applies again from there.

Shrink the box. Volumetric weight is driven entirely by outer dimensions, so every centimetre of void fill is a centimetre you pay for. The usual fixes, roughly in order of impact:

• Right-size your packaging. A small range of box sizes matched to your best sellers beats one big box for everything.
• Choose the carrier by parcel profile. A 4000 divisor punishes bulky, light goods far harder than a 5000 one.
• Check how your 3PL packs. Over-boxing and excess dunnage are common, and they show up as volumetric surcharges on every order.
• Negotiate the divisor. Higher-volume accounts can sometimes agree a more favourable divisor or a cap on dimensional charges.