Choosing a box that is too big wastes filler and raises courier charges through volumetric weight. A box that is too small crushes the product or bursts in transit. The right box size protects the item at the lowest cost. This guide explains a simple method to choose the right box size, with our free Box Size Calculator to do the maths.
Step 1: Measure the product
Measure the longest length, width and height of the product, including handles, caps or any part that sticks out. Use centimetres for accuracy.
Step 2: Add a padding allowance
Decide how much cushioning the item needs on each side:
| Product type | Padding per side |
|---|---|
| Books, clothes, soft goods | 0 to 1 cm |
| Boxed electronics, cosmetics | 2 to 3 cm |
| Glass, ceramics, fragile items | 5 cm or more |
Add the padding to both sides of each dimension. A product 30 × 20 × 10 cm with 3 cm padding needs an inner box of 36 × 26 × 16 cm.
Step 3: Inner vs outer dimensions
Box makers usually quote inner dimensions, the space available inside. Outer dimensions are larger by the board thickness: roughly 0.3 to 0.5 cm per side for single-wall (3-ply) board and 0.6 to 1 cm for double-wall (5-ply). Couriers charge on outer dimensions. Read inner vs outer box dimensions.
Step 4: Check volumetric weight
Couriers charge the higher of actual weight and volumetric weight. For a 36 × 26 × 16 cm box with a divisor of 5,000, volumetric weight = 36 × 26 × 16 ÷ 5,000 = 3.0 kg. If the product weighs 1 kg, you pay for 3 kg. Check with the Volumetric Weight Calculator.
Step 5: Choose a standard size
Custom boxes cost more in small quantities. Choose the nearest standard size from your supplier that fits the inner dimensions without large gaps.
Step 6: Fill the gaps
Any remaining space should be filled so the product cannot move. Estimate filler with the Bubble Wrap Calculator.
Common mistakes
- Measuring the product without its retail packaging
- Ignoring board thickness
- Using one big box for all orders
Multiple items
For several products in one box, arrange them to minimise empty space, then measure the bundle as one block.
Frequently asked questions
How much space should I leave around a product?
About 2 to 3 cm for most items, and 5 cm or more for fragile goods.
Do couriers use inner or outer box dimensions?
Outer dimensions.
Why does a big box cost more to ship?
Couriers charge volumetric weight when it is higher than actual weight.