What is a CBM Calculator?
The CBM calculator computes total volume in cubic meters from box dimensions and quantity. It is the standard basis for ocean freight LCL pricing.
How it's calculated
CBM = length(m) × width(m) × height(m) × quantity. In ocean freight, 1 CBM is conventionally treated as 1,000 kg when comparing volume against weight.
Worked example
Example: 100 boxes, each 50×40×30cm
- Volume per box: 0.5×0.4×0.3 = 0.06 m³
- Total CBM: 0.06 × 100 = 6 CBM
- Weight-ton equivalent: 6 CBM × 1,000kg = 6,000kg — if actual weight exceeds this, freight is priced by weight instead
Real-world sources of error
- Box measurement error: If boxes aren't perfectly rectangular or are slightly overpacked, measured CBM can exceed the calculated value.
- Palletizing gaps: Once boxes are stacked on pallets, unavoidable gaps often push actual shipped CBM 5-10% above the calculated figure.
- Carrier minimum billing units: A calculated 5.3 CBM may still be rounded up to the nearest 0.1 CBM depending on the carrier's billing policy.
Why is freight priced by volume?
A ship has two real constraints: it can run out of space, or it can run out of weight capacity. So freight is priced on whichever is greater — volume or weight. This is called Revenue Ton (R/T): R/T = max(CBM, weight in tons). Light, bulky cargo like pillows gets priced by volume; small, heavy cargo like steel gets priced by weight.
Good to know
- Air freight uses a different formula. Volumetric weight for air is length×width×height(cm) ÷ 6,000, converted to kg — air freight is far more sensitive to volume than ocean freight.
- LCL (less-than-container-load) shipments are billed by CBM, but anything under 1 CBM is usually rounded up to a full 1 CBM minimum charge.
- Box dimensions must always be measured outside dimensions. Using interior dimensions understates the true volume and throws off quotes.
- Once total volume passes roughly 15 CBM, booking a full container (FCL) often becomes cheaper than paying LCL rates.
- A 20-foot container has an internal capacity of about 33 CBM, but real-world loads typically only achieve about 28 CBM due to box shapes and stacking gaps.
Frequently asked questions
Q. How many kilograms is 1 CBM?
In ocean freight, 1 CBM is conventionally treated as 1,000 kg for comparison purposes — it is a billing reference, not an actual weight.
Q. What is R/T?
Revenue Ton — the greater of CBM or weight tons, used to calculate freight charges.
Q. Does reducing volume always lower shipping cost?
Not if weight is the binding constraint. Check which factor (volume or weight) determines your rate first.