Choosing the right packaging size sounds simple, but knowing how to calculate packaging size correctly helps you choose suitable poly mailers, corrugated cartons, and mailer boxes.
For poly mailers, product thickness affects the required bag width and length. For corrugated cartons and mailer boxes, board thickness and box structure determine the difference between inner and outer dimensions.
This guide shows you how to calculate the right packaging size for poly mailers, regular corrugated shipping cartons, and mailer boxes using simple formulas and practical examples.
How to Calculate Packaging Size for Poly Mailers
When choosing a poly mailer, don’t simply match the bag size to the length and width of your product. The product height also takes up space when the item is placed inside the bag.
Bag Width ≥ Product Width + Product Height + 2 cm
Bag Length ≥ Product Length + Product Height + 2 cm + 5 cm sealing flap
Example: For a product measuring 30 × 20 × 5 cm, the calculated bag width is 27 cm and the total bag length is 42 cm. The recommended size is therefore approximately 27 × 42 cm.
Corrugated Carton Inner and Outer Dimensions
When calculating corrugated carton dimensions, it is important to distinguish between the inner size and the outer size. The inner size refers to the usable space inside the carton, while the outer size is the actual finished size of the box.
For regular corrugated shipping cartons, the outer length and width are mainly affected by the board thickness, while the height increase is slightly different because of the carton folding structure.
Typical size increase:
3-Ply B Flute: +0.6 cm length, +0.6 cm width, +1.0 cm height
3-Ply C Flute: +0.8 cm length, +0.8 cm width, +1.2 cm height
5-Ply BC Flute: +1.5 cm length, +1.5 cm width, +2.0 cm height
Example: For a 5-ply BC flute carton with an inner size of 40 × 30 × 20 cm, the approximate outer size is 41.5 × 31.5 × 22 cm.
Mailer Box Inner and Outer Size Conversion
Mailer boxes have a different folding structure from regular shipping cartons, so their inner-to-outer size conversion is also different. Common corrugated boards for mailer boxes include E, B, C, and EB flute, from thinner to thicker.
Typical size increase:
E Flute: +1.0 cm length, +0.3 cm width, +0.3 cm height
B Flute: +1.7 cm length, +0.6 cm width, +0.6 cm height
C Flute: +2.2 cm length, +0.7 cm width, +0.7 cm height
EB Flute: +2.7 cm length, +0.9 cm width, +0.9 cm height
Example: For a B-flute mailer box with an inner size of 20 × 15 × 5 cm, the approximate outer size is 21.7 × 15.6 × 5.6 cm.
Frequently Asked Questions
How do I choose the right poly mailer size?
Measure the length, width, and height of your product. Product thickness should be considered when calculating both the bag width and length. Leave some extra space for easy packing and include the sealing flap when calculating the total bag length.
What is the difference between carton inner and outer dimensions?
Inner dimensions refer to the usable space inside the carton, while outer dimensions refer to the actual finished size of the box. When ordering custom cartons, always confirm whether the dimensions provided are inner or outer dimensions.
Does corrugated flute thickness affect box dimensions?
Yes. The thicker the corrugated board, the greater the difference between the inner and outer dimensions. For example, a 5-ply BC flute carton generally has a larger size increase than a 3-ply B or C flute carton.
Why is the height increase different for regular shipping cartons?
For regular corrugated shipping cartons, the length and width increase is mainly related to the board thickness. The height is also affected by the carton folding structure, so it cannot be calculated simply by adding twice the board thickness.
Need Help Choosing the Right Packaging Size?
If you are unsure which poly mailer, corrugated carton, or mailer box size is right for your product, send us your product dimensions and weight. We can help recommend a suitable packaging size, material, and corrugated flute based on your shipping requirements.