BCT stands for Box Compression Test or box compression strength. It represents the vertical compressive load a box can resist under test conditions before failure or a specified deformation limit.

ECT stands for Edge Crush Test. It measures the edgewise compressive strength of corrugated board and is one of the main inputs in the simplified McKee equation.

Is the McKee formula accurate for all boxes?

No. It works best as a first-pass estimate for regular slotted corrugated containers. Different box styles, die cuts, hand holes, interior supports, very tall boxes, humidity, and pallet patterns can make the result inaccurate.

Why add a humidity or damage reduction?

Corrugated strength can drop after moisture exposure, long storage, rough handling, and crushing during conversion or shipping. A reduction factor helps avoid treating ideal lab strength as real distribution strength.

Should I still do a physical compression test?

Yes for important packaging decisions. McKee estimates help with early design, but ASTM-style compression testing with the actual box, contents, closure, and conditioning gives more reliable evidence.

Engineering

Box Compression Test Strength Calculator

Estimate corrugated box compression strength using the simplified McKee equation, then compare it with an expected stacking load and safety factor.

This calculator is intended for regular slotted corrugated containers using ECT, board caliper, and perimeter. Actual BCT testing is still needed for critical packaging because humidity, handling damage, box style, contents, and pallet pattern affect performance.

ECT (lb/in)

Board caliper / thickness (in)

Box length L (in)

Box width W (in)

Box gross weight (lb)

Boxes stacked above this box

Safety factor

Strength reduction for humidity/damage (%)

Box compression estimate

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Raw McKee BCT—

Adjusted strength—

Required stacking resistance—

Pass / margin—

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How the McKee BCT estimate works

The simplified McKee equation estimates corrugated box compression strength from edge crush test value, board caliper, and box perimeter. It is widely used for first-pass RSC-style box estimates, but it is not the same as a lab compression test.

A peer-reviewed packaging study notes that McKee’s equation is a well-known semi-empirical formula for estimating stacking load, while ASTM D642 covers actual compression tests on shipping containers. See the open-access paper on corrugated box compression strength estimation and the ASTM page for D642 compression testing of shipping containers.

Worked example

ECT = 32 lb/in Caliper = 0.16 in Length = 16 in, width = 12 in Perimeter = 2(16+12) = 56 in BCT = 5.87 × 32 × √(0.16 × 56) = about 562 lb

After a 25% reduction for humidity and handling damage, the usable estimate becomes about 421 lb. That adjusted value should be compared with the expected stacked load times a safety factor.

Common mistakes in box compression estimates

Do not use the box height in the simplified McKee equation unless you are using a different model that includes it. Do not ignore humidity, pallet overhang, poor stacking alignment, hand holes, print crush, die cuts, or damage from distribution. These can reduce real stacking performance significantly.

Common questions

BCT stands for Box Compression Test or box compression strength. It represents the vertical compressive load a box can resist under test conditions before failure or a specified deformation limit.
ECT stands for Edge Crush Test. It measures the edgewise compressive strength of corrugated board and is one of the main inputs in the simplified McKee equation.
No. It works best as a first-pass estimate for regular slotted corrugated containers. Different box styles, die cuts, hand holes, interior supports, very tall boxes, humidity, and pallet patterns can make the result inaccurate.
Corrugated strength can drop after moisture exposure, long storage, rough handling, and crushing during conversion or shipping. A reduction factor helps avoid treating ideal lab strength as real distribution strength.
Yes for important packaging decisions. McKee estimates help with early design, but ASTM-style compression testing with the actual box, contents, closure, and conditioning gives more reliable evidence.