What Is OEE and How Is It Measured?

“You can’t improve what you don’t measure.”

This principle holds especially true in the world of manufacturing, where performance, reliability, and continuous improvement are critical. One of the most powerful metrics used to track and improve manufacturing efficiency is Overall Equipment Effectiveness, or OEE.

In this article, we’ll break down what OEE is, how it’s calculated, and why it matters, especially for maintenance and reliability teams aiming to reduce downtime and improve asset performance.

The Definition of OEE

Overall Equipment Effectiveness is a key performance indicator (KPI) used in manufacturing to measure equipment efficiency. It helps organizations identify where and how productivity is lost so they can target improvement efforts more effectively.

OEE is a performance metric that is expressed as a percentage, where:

• 100% means perfect production: only good parts, as fast as possible, with no downtime.
• Anything below 100% reflects losses in availability, performance, or quality.

By using OEE, manufacturers can uncover hidden inefficiencies, improve equipment reliability, and align production goals with maintenance strategies.

Why OEE Matters for Maintenance and Reliability

For reliability engineers and maintenance managers, Oeverall Equipment Effectiveness is a goldmine of insight.

It highlights hidden losses that chip away at operational efficiency. OEE data can be used to:

• Pinpoint chronic equipment failures
• Justify investments in condition-based or predictive maintenance
• Prioritize assets and production lines for improvement
• Track the ROI of maintenance and reliability initiatives
• Compare internal performance against industry benchmarks

The Three Pillars of OEE

Overall Equipment Effectiveness is built upon three fundamental metrics: Availability, Performance, and Quality. Each pillar addresses a different type of loss that affects equipment effectiveness.

Pilar	What it Measures	Formula
Availability	Percentage of total available time the equipment was running	Run Time / Total Available Production Time
Performance	Actual running speed vs. ideal running speed	(Ideal Cycle Time × Total Count) / Run Time
Quality	Good parts produced vs. total parts produced	Good Count / Total Count

Availability: Downtime vs. Total Potential Time

Availability measures how much of the total time your plant is open is actually running equipment.

This includes all time the facility is operational, even when equipment is not scheduled because of breaks, changeovers, or routine maintenance. These are still considered lost opportunities and should be counted in the OEE calculation formula.

Example:

If your company operates 16 hours per day, 7 days a week, your total weekly availability is:

16 × 7 = 112 hours

If a machine experiences 12 hours of total downtime during that week (including breakdowns, planned maintenance, and idle time), the run time is:

Run Time = 112 – 12 = 100 hours

So Availability = 100 / 112 = 89.3%

Performance: Speed Losses

Performance looks at whether equipment is running at its ideal speed when it is operational. Even if the machine is running continuously, it may still be underperforming.

Let’s say a machine should ideally produce 1 part every 60 seconds (i.e., 60 parts per hour), but operators slow it down to 80% of its capability for safety or process stability reasons. That speed loss impacts your OEE.

Performance = (Ideal Cycle Time × Total Count) / Run Time

Even if the machine is “on,” running below its potential still costs production loss.

Quality: Defect Rates

Quality measures the percentage of units produced that meet quality standards. Any rework, scrap, or rejected units reduce this score.

Quality = Good Count / Total Count

For instance, if 980 out of 1,000 units pass inspection, then:

Quality = 980 / 1000 = 98%

How to Calculate OEE (With Example)

The measurement of OEE (Overall Equipment Effectiveness) takes into account three key factors that equally influence the final score: Availability, Performance, and Quality. Each of these factors represents a different type of loss in a manufacturing process and helps identify where efficiency is being lost.

• Availability reflects downtime losses
• Performance addresses speed losses
• Quality considers quality losses

These three factors are multiplied together to calculate the OEE:

OEE = Availability × Performance × Quality

OEE Example calculation:

• Availability = 90%
• Performance = 95%
• Quality = 98%

Then:

OEE = 0.90 × 0.95 × 0.98 = 0.8379

0.8379 x 100 = 83,79%

This means that only 83.79% of the total available production time resulted in good parts, at the right speed, with no interruptions.

Measuring OEE in practice

Here’s how to apply the calculation in real life:

Step 1: Define Total Available Time

Start with the full number of hours your facility is open, regardless of planned or unplanned production. If the plant runs 3 shifts, 7 days a week, that’s your baseline.

Step 2: Track All Downtime

Every moment your equipment isn’t producing during that open time is an Availability loss. Include:

• Equipment breakdowns
• Setup or changeovers
• Waiting for materials
• Maintenance (even planned)
• Operator absence

Step 3: Monitor Performance Losses

Compare the actual output rate to the ideal rate. If the machine is slowed down intentionally or because of wear, this should be recorded.

Example: Your machine can run at 100 RPM, but you operate it at 80 RPM for stability. That’s a 20% loss in performance, even if it’s running all shift.

Step 4: Record Quality Losses

Track how many parts are scrapped, reworked, or rejected. These reduce the value your equipment is delivering.

Common Misconceptions About OEE

“OEE and maintenance doesn’t go together”

OEE may be tracked by operations, but it directly reflects equipment condition, failure patterns, and maintenance efficiency.

“We need to hit 100% OEE”

In theory, yes. But in practice, it’s nearly impossible. Instead, aim for steady improvement and build your maintenance strategy based on your goals, Asset Criticality Rankign and risk mitigation so you know how much and where you should invest to improve OEE.

“Measuring OEE is too complex”

You can start simply, with a spreadsheet, a whiteboard, or by tracking only critical assets. But digital tools like an APM can automate data capture and reporting for deeper insights.

Tips for Getting Started with OEE

• Begin with one critical machine or line
• Use a standard definition of OEE across teams (availability includes all open hours!)
• Automate data collection if possible
• Don’t use OEE to assign blame, it’s a diagnostic tool, not a scorecard

Conclusion

OEE is more than just a number. It’s a powerful lens through which you can evaluate equipment performance, identify weaknesses, and drive continuous improvement.

By measuring OEE against your plant’s full operating window you get a much clearer picture of where efficiency is lost and where reliability efforts should focus.

Frequently Asked Questions (FAQ)

What’s a good OEE benchmark for my industry?

85% is often cited as a “world-class” OEE, but this varies according to your sector. Benchmark can be found online.

What tools or systems can help automate OEE measurement?

An APM (Asset Performance Management) platforms or CMMS systems, can facilitate data collection. But the APM can also provide dashboards for tracking OEE in real time.

What’s the difference between OEE vs asset utilization?

Asset utilization measures how often an asset is used relative to its full capacity. OEE, on the other hand, measures how effectively the asset is used, considering downtime, speed, and quality.

What are some typical root causes of low OEE?

• Equipment failures or poor maintenance planning
• Frequent changeovers or long setup times
• Operator errors
• Substandard raw materials
• Lack of spare parts or delayed maintenance