In the ready-made garment (RMG) industry, packaging is the final stage of manufacturing but one of the most critical for logistics. Merchandisers must estimate the total shipment CBM (Cubic Meters) to book container spaces (FCL/LCL) and calculate empty carton weights to declare gross weights on shipping bills. Underestimating packaging volume leads to containers getting left behind at the port, while overestimating wastes expensive shipping budget. This guide covers the complete formulas needed for carton logistics.
1. Calculating Carton Count & Shipment CBM
Cubic Meter (CBM) represents the volume occupied by the carton. To calculate CBM for a shipment, you must know the cartoon dimensions (Length × Width × Height) and the total carton count based on the packing list ratio:
Total Cartons = Math.ceil(Order Quantity / Garments per Carton) CBM per Carton (m³) = [Length (cm) × Width (cm) × Height (cm)] / 1,000,000 Total Shipment CBM = CBM per Carton × Total Cartons
2. The Corrugated Board Empty Weight Formula
Exporters must declare the gross weight of shipments (garments + packaging). To find the empty weight of a carton, we calculate the blank area of the sheet used to fold the box, factoring in joints (3-5 cm) and flap closures (2-3 cm):
Blank Length (cm) = (Length + Width) × 2 + 5 (Joint) Blank Width (cm) = Width + Height + 3 (Flap) Blank Area (sqm) = (Blank Length × Blank Width) / 10,000 Empty Carton Weight (grams) = Blank Area (sqm) × Total Board GSM Where: · Total Board GSM = Outer Liner GSM + (Flute GSM × Flute Factor × Flutes) + Mid Liners + Inner Liner GSM · Flute take-up factor is typically 1.40 for standard fluting.
Board Structure & GSM Accumulation
| Ply Count | Board Structure | GSM Accumulation Formula |
|---|---|---|
| 3-Ply | L1 (Outer) + Flute + L2 (Inner) | Outer GSM + (Flute GSM × 1.4) + Inner GSM |
| 5-Ply | L1 + Flute1 + Mid + Flute2 + L2 | Outer + (Flute × 1.4 × 2) + Mid Liner GSM + Inner |
| 7-Ply | L1 + Flute1 + Mid1 + Flute2 + Mid2 + Flute3 + L2 | Outer + (Flute × 1.4 × 3) + Mid Liners (2) + Inner |
3. Volumetric Weight for Air Freight Surcharges
Air freight forwarders charge based on dimensional weight if the carton is lightweight but bulky. The industry standard divisor is 5000 for kg calculations:
Volumetric Weight (kg) = (Length in cm × Width in cm × Height in cm) / 5000 If the volumetric weight exceeds the actual gross weight, the carrier bills you at the volumetric rate.
4. References and Shipping Standards
Corrugated box weight calculations align with TAPPI (Technical Association of the Pulp and Paper Industry) testing standards and packaging guidelines from the international Federation of Corrugated Board Manufacturers (FEFCO). Always run laboratory compression tests to verify stacking strength.