PMI, or Purchasing Managers’ Index, is a monthly survey-based indicator of whether business conditions are improving, worsening or holding steady. Businesses can use it to revisit inventory and purchasing assumptions, but a national or sector-wide PMI is context—not a forecast of a particular company’s demand or a formula for how much to order.
What does PMI measure?
PMI is built from monthly reports by business executives. Depending on the provider, geography and sector, its component measures can include new orders, output or business activity, employment, supplier delivery performance, purchasing, backlogs, inventories and prices. S&P Global describes measures spanning manufacturing and services, while the Institute for Supply Management (ISM) publishes separate U.S. manufacturing and services reports. S&P Global’s PMI overview, its PMI FAQ and ISM’s report page describe their respective series.
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PMI is generally a diffusion measure: it summarizes whether respondents report conditions improving, worsening or staying the same compared with the previous month. It is not a direct count of goods in stock, output or sales. A reading of 52, for example, does not mean output grew by 52%.
What the ISM Manufacturing headline combines
In the ISM Manufacturing PMI, the composite equally weights five component indexes: New Orders, Production, Employment, Supplier Deliveries and Inventories. This is the ISM methodology, not a universal recipe used by every PMI producer. ISM says a reading above 50% indicates general expansion in the manufacturing economy and a reading below 50% indicates general decline. The threshold describes the direction of reported conditions, not the rate of economic growth. ISM’s methodology explains the components and interpretation.
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What does a PMI reading below 50 mean?
For the ISM Manufacturing PMI, a reading below 50% means the manufacturing economy is generally declining according to the survey’s diffusion measure. It does not mean every manufacturer is shrinking, nor does it quantify how much a particular business’s sales or output has fallen. Check which PMI and which component you are reading: “below 50” should not be generalized to every provider’s series or treated as a company-specific demand signal.
How can a business use PMI to plan inventory and purchasing?
Use the report to prompt a review of assumptions, then make buying decisions from your own demand and inventory data. S&P Global identifies monitoring inventory and price trends as uses of PMI data, and ISM presents its reports as guidance for supply management and business leaders. Neither provides a universal formula that converts a national PMI reading into a company’s order quantity.
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- Choose the relevant series. Match the report to the geography and sector that most closely reflect your customers, suppliers or production environment. Note the provider, reference month and whether you are looking at the headline or a sub-index.
- Read related indicators together. Look at new orders or activity alongside inventories and supplier deliveries. A stronger orders measure may justify reviewing replenishment assumptions and supplier capacity; it is not, by itself, a reason to increase purchase quantities.
- Check your actual position. Compare the broad signal with company sales and orders, on-hand stock, committed stock and open purchase orders. Account for seasonal patterns and firm customer commitments that may not match the wider trend.
- Review timing and exposure. If demand-related measures weaken, reassess planned purchase timing and the risk and carrying cost of excess stock. If they strengthen, check whether current stock and confirmed demand support a change in replenishment.
- Interpret delivery signals carefully. Slower supplier deliveries can reflect demand pressure or supply constraints. Either may affect lead-time assumptions, so compare the PMI signal with your suppliers’ actual lead times before changing buffers.
- Make the decision against service goals. Reconcile any adjustment with your service-level targets, supplier capacity and the cost of stockouts versus holding inventory. Use PMI as one input rather than an automatic order trigger.
How to compare PMI readings without mixing unlike series
Before comparing two readings or building a trend, align the provider, geography, sector, reference month and measure (headline or sub-index). Also check seasonal-adjustment status. ISM’s methodology specifies seasonal adjustment for selected component indexes, and ISM announced annual updates effective with its January 2026 reports. ISM’s seasonal-adjustment information describes those factors. Treat differences between providers as possible differences in methodology or survey scope unless you have verified that the series are comparable; do not splice them together as if they were identical. S&P Global’s PMI FAQ provides information about its series.
When citing a reading internally, name its producer, geography, sector, reference month and component. This prevents an ISM U.S. manufacturing headline, for example, from being mistaken for an all-economy measure or for a reading from another provider.
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