Calculate corrugated box compression strength from ECT, box dimensions, and board thickness, or solve for the required ECT, in imperial or metric units.

Simplified McKee estimate for corrugated boxes. Use measured combined-board caliper when available; flute presets are approximate.

Combined-board thickness, including facings.

Stacking factor

Optional, at least 1. Divides estimated BCT by this factor; it is not a certified safe working load.

Box Crush Test (BCT) Formula

The following formula is used to calculate the Box Crush Test (BCT). 

BCT = 5.876 × ECT × SQRT(P × T)

Variables:

  • BCT is the estimated box compression strength (lbf)
  • ECT is the edge crush strength (lbf/in)
  • P is the box perimeter (in) 
  • T is the measured combined-board caliper, including facings (in)

This simplified McKee equation estimates compression strength for conventional corrugated boxes. Its buckling assumptions are most appropriate for regular slotted containers with box height at least perimeter ÷ 7. It does not certify a safe stacking load. Moisture, damage, construction, support and storage time affect performance; verify the actual package by testing. Flute presets are approximate total calipers; use measured board thickness when available.

How to Calculate Box Crush Test (BCT)?

The following steps outline how to calculate the Box Crush Test (BCT).

  1. First, determine the edge crush test (ECT).
  2. Next, determine the box perimeter (in). 
  3. Next, determine the box thickness (in). 
  4. Next, gather the formula from above = BCT = 5.876*ECT*SQRT(P*T).
  5. Finally, calculate the Box Crush Test (BCT).
  6. After inserting the variables and calculating the result, check your answer with the calculator above. 

Example Problem:

Use the following variables as an example problem to test your knowledge.

edge crush strength (ECT) = 32 lbf/in

box perimeter (in) = 40

board caliper (in) = 0.16

BCT = 5.876 × 32 × √(40 × 0.16) ≈ 475.7 lbf (2.116 kN).