The mechanism
A corrugated boxes escalation clause indexes the portion of the contract price tied to corrugated boxes to a published series instead of fixing it at signing. The benchmark is the BLS producer price index for Corrugated Shipping Containers, series WPU09150301.
Corrugated boxes is a real input cost in packaging and shipping, e-commerce fulfilment, and food and beverage distribution work. Its price can move further over a contract term than a fixed-price contingency is built to absorb, so indexing it moves that risk onto the published series instead of onto one party.
What's specific to corrugated boxes
A box price is the board it is made from plus converting and freight. This index follows the corrugated board price closely but moves by less, because converting costs sit on top. A clause on a broad paper series misses the board-to-box link.
Sources: WPU09150301 (Corrugated Shipping Containers); BLS WPU091405.
Since 2016, this index has followed the corrugated board price index in the same month and moved about two thirds as far as it over a year.
Over the 12 months to Sep 2026, the corrugated board price index rose 7.9% and this index rose 8.9%.
The box index follows the board index in direction, with a damped size. If you buy both board and boxes, escalating each on its own series double counts the board move.
The calculation, step by step
- Base index value. The index value at the base period, usually the month of contract signing or bid submission.
- Current index value. The index value at the adjustment date, usually the month of delivery or invoicing.
- Ratio. Current value divided by base value.
- Adjustment. Apply the ratio to the portion of the contract price tied to corrugated boxes only.
Take a contract signed in September 2025 with $240,000 of corrugated boxes scope, invoiced in September 2026.
| Base index, Sep 2025 | 357.173 |
| Current index, Sep 2026 (revisable) | 388.939 |
| Ratio, 388.939 ÷ 357.173 | 1.0889 |
| Amount at signing | $240,000 |
| Adjustment added to that amount | +$21,345 |
Live figures from the stored series, updated when the provider publishes. Sep 2026 can still be revised, so a clause should say whether the invoice uses the first published value or is trued up later.
Where clauses go wrong
BLS publishes other series a corrugated boxes clause could be read against, and they do not move together. A clause that only says "the corrugated boxes index" leaves the two sides to pick different ones.
Over the 12 months to Sep 2026, these series moved differently. On the same $240,000, the gap between the highest and lowest is $25,199.
| Series | What it covers | 12 months | On $240,000 |
|---|---|---|---|
WPU09150301 | Corrugated Shipping Containers | +8.9% | +$21,345 |
PCU32221132221102 | Corrugated and Solid Fiber Box Manufacturing, Corrugated Shipping Containers for Paper and Allied Products | +8.9% | +$21,241 |
WPU091405 | Corrugated Paperboard in Sheets and Rolls, Lined and Unlined | +7.9% | +$19,071 |
WPU09120325 | Corrugated Recyclable Paper | +18.4% | +$44,270 |
Write the series code, WPU09150301, into the contract text, with the BLS title next to it.
The other gaps are the same as for any indexed input: no averaging window and no cap or floor.
Related
- Live WPU09150301 index page: the full history, a chart, and the values to copy.
- Escalation clause analyzer: paste a clause and see the formula, undefined terms, and risk score.
- How escalation clause base periods work
- Publication lag and revisions