ECT to Mullen: converting corrugated board grades
Corrugated board is specified two ways, and buyers constantly need to convert between them. Mullen (or burst) rates how much pressure the board resists before it punctures; ECT (edge crush test) rates how much edge-wise load it takes before it crushes. There is no exact formula from one to the other — they measure different things — so the industry uses a published equivalence table from the Fibre Box Association that pairs each Mullen grade with a minimum ECT that carries roughly the same duty. A 200# burst board, for example, is commonly equivalent to about 32 ECT.
Which spec should you actually use?
They protect against different failures, so the right one depends on your risk. Burst matters when boxes take rough handling, drops, and punctures. ECT matters when boxes stack — on a pallet, in a warehouse, in a trailer — because ECT feeds directly into box compression strength (BCT). Most modern shipping specs have moved to ECT for exactly this reason: it predicts the failure that flattens a pallet. If your boxes stack, spec ECT and verify the stack with a compression calculation.
Why ECT can use lighter board
An ECT grade can often be met with less fiber than the equivalent burst grade, because ECT rewards efficient board construction rather than raw basis weight. That’s part of why converting matters: speccing "200# equivalent" as 32 ECT can lower board weight and cost while keeping the stacking performance you need. Convert the grade, then confirm the box holds its stack.
Questions
What is 200# board equivalent to in ECT?
About 32 ECT for single wall, per the Fibre Box Association equivalence table. The pairing means a 32 ECT board carries roughly the same duty as a 200# burst board for typical shipping, though the two specs measure different things — burst resists puncture, ECT predicts stacking strength.
Is there a formula to convert ECT to Mullen?
No exact formula — they measure different properties, so the industry uses a published equivalence table rather than a calculation. This tool looks up the standard Fibre Box Association pairing for single and double wall. Treat the equivalent as a minimum, not a precise conversion.
Should I spec ECT or Mullen for my boxes?
Spec ECT if your boxes stack — on pallets, in warehouses, in transit — because ECT predicts compression (stacking) strength directly. Spec or keep an eye on Mullen (burst) if your boxes take rough handling, drops, and punctures. Many modern shipping specs use ECT because stacking is the common failure mode.
Why does ECT board sometimes weigh less than the Mullen equivalent?
Because ECT rewards efficient board construction rather than raw basis weight, an ECT grade can often be met with less fiber than the equivalent burst grade. Converting a burst spec to its ECT equivalent can therefore lower board weight and cost while keeping stacking performance — as long as you verify the box still holds its stack.
How do I know if my box is strong enough after converting?
Take the ECT grade and estimate box compression strength (BCT) with the McKee formula, using your box dimensions and the safe stack load. The ECT-to-Mullen conversion sets the board; the compression estimate confirms the finished box survives the stack it will see.
Spec the right board, once.
We quote corrugated on the grade that matches your real stacking and handling — not an over-built default.