Choosing a flute
Choose a coarse flute (C, or A where available) when the box must stack, a fine flute (E or F) when it must print well or save space, B in between for die-cut and dense goods, and a double wall when one wall is not enough.
The trade in one table
At the same ECT and size, McKee rates strength by the square root of caliper. The table shows how each flute compares with C flute and how much it adds to outside dimensions.
| Board | Caliper, in | Strength vs C, same ECT | Added to L and W |
|---|---|---|---|
| A flute | 0.188 | 110% | 0.375 in |
| B flute | 0.125 | 89% | 0.25 in |
| C flute | 0.156 | 100% | 0.313 in |
| E flute | 0.063 | 63% | 0.125 in |
| F flute | 0.031 | 45% | 0.063 in |
| BC double wall | 0.281 | 134% | 0.563 in |
| EB double wall | 0.188 | 110% | 0.375 in |
| AC double wall | 0.344 | 148% | 0.688 in |
| AAC triple wall | 0.531 | 184% | 1.063 in |
Questions to ask
- Will the box sit in a stack for weeks? Favour thickness.
- Is the outside printed with fine graphics? Favour more flutes per foot.
- Does the product push on the walls? Favour B or a double wall for crush and puncture resistance.
- Is pallet or trailer space tight? Thinner board means smaller outside dimensions.
Use it
- Flutes
- B flute vs c flute
- C flute vs e flute
- Inside outside dimensions
- Spec Builder
- Right-sizing boxes to cut dimensional weight
- Reading a box maker's certificate
- Stacking strength and safety factors
Last reviewed 2026-10-27. Formulas and sources: method, sources.