What is volumetric weight?
Carriers price shipments by space as well as mass. A large, light box takes up room on a van or plane that could carry heavier parcels, so carriers calculate a volumetric (dimensional) weight from the box size and bill whichever is greater: actual or volumetric. That figure is the chargeable weight.
The formula
volumetric weight = length × width × height ÷ divisor
- Metric: dimensions in centimetres, result in kilograms. Divisor 5000 is common for express and international parcels; 6000 is the IATA standard for air cargo.
- Imperial: dimensions in inches, result in pounds. Divisor 139 is common for US domestic parcel services; some services use 166.
Divisors and rounding rules differ by carrier, service and contract. Always confirm the current divisor in your carrier's rate guide, since negotiated accounts often have custom values.
Worked example
A 40 × 30 × 20 cm box weighing 4 kg: 24,000 cm³ ÷ 5000 = 4.8 kg volumetric. Because 4.8 kg is more than the 4 kg actual weight, you're billed for 4.8 kg, which most carriers round up to 5 kg.
How to reduce chargeable weight
- Choose the smallest box that protects the item; measure at the widest points, including bulges.
- Use flat-pack or poly mailers for soft goods.
- Consolidate small items into one well-filled carton instead of several half-empty ones.
- Ask about divisors when negotiating rates: a move from 5000 to 6000 cuts volumetric weight by about 17%.