ABC/XYZ inventory classification for small manufacturers

A typical manufacturer has hundreds or thousands of purchased parts, and nobody has time to watch them all closely. ABC/XYZ classification is a simple way to decide where attention pays off. It sorts items by how much they are worth and by how predictable their demand is. This guide explains how to do it with a spreadsheet.

ABC: sorting by value

ABC classification ranks items by their annual consumption value, which is annual usage multiplied by unit cost. It is based on the familiar pattern that a small share of items usually accounts for a large share of value.

How to do it

• Export each item’s annual usage and unit cost.
• Multiply them to get annual consumption value.
• Sort the list from highest to lowest value.
• Calculate the cumulative percentage of total value as you go down the list.
• Assign classes based on cumulative value.

A common starting point is: A items make up roughly the top 80% of value, B items the next 15% and C items the final 5%. These cut-offs are conventions, not rules. Adjust them so that the A class is small enough to manage closely.

XYZ: sorting by predictability

XYZ classification ranks items by how stable their demand is. The usual measure is the coefficient of variation, which is the standard deviation of demand divided by the average demand over the same periods.

How to do it

• Export monthly usage for each item, ideally for twelve months or more.
• Calculate the average and standard deviation of monthly usage.
• Divide the standard deviation by the average to get the coefficient of variation.
• Assign classes: X items have steady demand, Y items vary moderately and Z items are erratic.

As with ABC, the cut-offs are a judgment. Many teams start by treating a coefficient below about 0.5 as X and above about 1.0 as Z, then adjust after reviewing the results. Items with very few months of usage need separate review, because the calculation is unreliable for them.

Combining the two: the nine-box matrix

Putting ABC and XYZ together gives nine groups. Each group suggests a different planning approach:

• AX: high value, steady demand. Plan tightly, with low safety stock and frequent orders. These items reward careful attention.
• AY: high value, moderate variation. Review regularly and set safety stock with care.
• AZ: high value, erratic demand. Consider making to order, working closely with customers on forecasts or agreeing on supplier stock programs.
• BX, BY: medium value. Use standard reorder points and review them periodically.
• BZ: medium value, erratic. Review individually; some may be candidates for make-to-order.
• CX, CY: low value. Use simple rules, such as larger order quantities and generous safety stock, to reduce ordering effort.
• CZ: low value, erratic. Often candidates for review or removal, especially if usage has stopped.

Using the results

Classification is only useful if it changes how you plan. Practical uses include:

• Setting different service levels by class in your safety stock calculations
• Reviewing reorder points more often for A items
• Choosing order quantities with EOQ vs MOQ in mind for C items
• Focusing cycle counts on A items
• Flagging CZ items for a dead stock review

Common pitfalls

• Ignoring criticality: a cheap part that stops the line matters more than its value suggests. Add a critical flag for such parts.
• Never updating: usage changes. Recalculate the classes at least twice a year.
• Using too little history: a few months of data can make seasonal items look erratic.
• Treating the cut-offs as fixed: adjust them to fit your business.

Getting started

A spreadsheet is enough to run your first classification. Once you see the nine groups, you will usually find a few surprises, such as high-value items with no safety stock or low-value items being ordered every week. For all of our formula guides and calculators, visit the free supply chain tools page. If you would like help applying the results, see inventory optimization consulting.

Frequently asked questions

Can we do ABC/XYZ in Excel?

Yes. The method uses only multiplication, sorting, running totals, averages and standard deviations, all of which Excel and similar spreadsheets handle well.

What about new items with no history?

Put them in a separate group and review them manually until you have enough history, usually several months.

Should we classify finished goods too?

Yes. The same method works for finished goods, and it can help you decide which products to make to stock and which to make to order.

How often should we reclassify?

At least twice a year, or more often if your product mix changes quickly.