01The four steps
Step 1 — Measure the packed parcel. Outer dimensions of the sealed, labelled parcel as it will travel: longest points on each axis, including bulges and protrusions. Carriers measure the object, not the paperwork — a carton that bulges measures as its bulged shape.
Step 2 — Apply carrier rounding
Most carriers round each dimension to the nearest whole centimetre or inch (some round up) before calculating. Prediction should use the same convention as your carrier's tariff, or your estimate will drift from the invoice by exactly the rounding.
Step 3 — Multiply and divide
Multiply L x W x H, then divide by the divisor for your carrier and service: 5000 or 6000 for cm-to-kg; 139 or 166 for inches-to-pounds. The result is dimensional weight. The calculator runs this step for you.
Step 4 — Compare and round up
Billable weight is the greater of dimensional and actual weight, typically rounded up to the carrier's billing increment (often the next 0.5 kg). That figure — not the scale weight alone — is what the parcel costs to ship.
02Worked examples
Read the bedding bale row twice: the same parcel bills 4 kg heavier on the express divisor than on the road divisor, and 18 kg heavier than its scale weight on both. That spread — divisor choice and packaging volume — is where dimensional-weight cost is actually decided. The concept guide covers the strategy; this page is the arithmetic.
Dimensional weight examples
| Parcel | Dimensions | Divisor | Dim weight | Actual | Bills at |
|---|---|---|---|---|---|
| Shoe box, apparel | 35 x 25 x 15 cm | 5000 | 2.63 kg | 0.9 kg | 2.63 kg (dim) |
| Dense parts carton | 40 x 30 x 25 cm | 5000 | 6.0 kg | 11 kg | 11 kg (actual) |
| Bedding bale | 60 x 50 x 40 cm | 5000 | 24.0 kg | 6 kg | 24.0 kg (dim) |
| Same bale, road service | 60 x 50 x 40 cm | 6000 | 20.0 kg | 6 kg | 20.0 kg (dim) |
| US parcel | 24 x 16 x 12 in | 139 | 33.2 lb | 12 lb | 33.2 lb (dim) |
03Common calculation mistakes
Using the empty box's nominal size instead of the packed parcel's measured size. Measuring the product instead of the packaging. Forgetting that carriers round before they multiply. Applying the express divisor to a road shipment (or the reverse) when comparing quotes. And the most expensive one: calculating diligently for the parcels you remember to check, while the stream ships unmeasured — the failure that turns a calculation habit into a dimensioner purchase.