Phase 2

Fluting & Box Crush Strength Advisor

Tell us how heavy your product is and how high your boxes get stacked. The McKee formula tells you the exact ECT board grade you need so they don't collapse in transit.

1. Per-box product weight

How much product is inside each box (kg or lb)?

2. Stack height

How many boxes high do they get stacked in the warehouse or truck?

Recommended board grade

Target top-load strength:

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Get 5 sample boxes in your recommended board grade shipped free so you can stress-test before committing.

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Free calculator using the McKee Formula to recommend the right corrugated flute (B, C, BC double-wall, EB) and ECT grade for your product weight, stack height and humidity — so boxes do not collapse in transit or storage.

What is the Box Flute & Crush Strength Advisor?

The McKee Formula is the industry-standard equation for predicting box compression strength (BCT) from the edge crush test (ECT) value of the corrugated board, board calliper and box perimeter. A box rated 32 ECT can hold roughly 100 lb of stacked load before failure at sea-level humidity. Get the flute wrong and you pay either in returns (under-spec) or in cardboard cost (over-spec).

How it works — in 4 steps

1
Enter your box dimensions. Internal length, width, depth and the product weight per box.
2
Tell us the stack. How many boxes will be stacked in the warehouse or on the pallet.
3
Pick storage humidity. Tropical (Brisbane, Singapore), temperate (Melbourne, London) or dry (Phoenix, Adelaide).
4
Get a flute & ECT spec. The advisor returns the recommended flute (B, C, BC, EB) and minimum ECT grade with a Safety Factor of 4.5 applied per FEFCO and TAPPI guidelines.

Who uses this calculator?

AU ecommerce 3PLs and warehouses palletising for retail distribution
US Amazon FBA prep centres avoiding ISTA-6 amazon.com failures
EU manufacturers shipping to Carrefour and Tesco distribution centres
Glass, ceramics, wine and homeware brands needing transit-safe packaging

Available in regions: Australia · United States · United Kingdom · Canada · New Zealand · European Union

Frequently asked questions

B flute (~3 mm) gives high crush resistance and good printability — typical for retail boxes. C flute (~4 mm) gives the best stacking strength for shipping cartons. BC double-wall combines both and is rated for heavy industrial loads up to ~75 kg per box.

For products under 5 kg, 32 ECT (single-wall C flute) is usually sufficient. 5–15 kg products need 44 ECT or BC double-wall. Above 15 kg you need 48 ECT or higher with edge-crush testing on each batch.

Corrugated fibreboard loses approximately 50 % of its compression strength at 90 % relative humidity vs 50 % RH. Tropical storage (Brisbane, Singapore) requires a 1.5×–2× safety factor over temperate-zone packaging.

FEFCO and TAPPI recommend a Safety Factor between 3 and 7 to account for storage time, humidity, vibration and pallet stack movement. We default to 4.5 (typical for 30-day warehouse storage in mixed climate) which is the same value used by Amazon and Coles supplier standards.

Amazon does not mandate a single ECT value but requires shipments to pass ISTA-6 Amazon.com testing. In practice that means 32 ECT minimum for single-item boxes under 5 kg and 44 ECT for multi-item or heavier shipments.

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