How to Calculate OEE (with Worked Example)

OEE is one of the few plant-floor metrics that can point directly at capacity losses — if you calculate it consistently.

What OEE is and why plants track it

Overall Equipment Effectiveness (OEE) is the percent of planned production time that turned into good parts at the ideal rate. It combines downtime, slow running, and scrap into one number so the team can see whether the constraint is availability, performance, or quality.

Good OEE is not a trophy number. It is a way to keep the conversation honest. If the line missed schedule, OEE tells you whether you lost the day to waiting on maintenance, running below rate, or making bad parts.

The OEE formula

OEE is the product of three factors:

• Availability = run time ÷ planned production time.
• Performance = (ideal cycle time × total parts) ÷ run time.
• Quality = good parts ÷ total parts.

Keep the units straight. If run time is in minutes and ideal cycle time is in seconds, convert ideal time to minutes before dividing.

Worked example: one 480-minute shift

Use the same defaults as the free calculator:

• Shift length: 480 minutes
• Breaks: 30 minutes
• Planned stops: 20 minutes
• Unplanned downtime: 47 minutes
• Ideal cycle time: 30 seconds per part
• Total parts: 766
• Good parts: 732

1. Planned production time

Breaks and planned stops are removed before calculating availability. They are not equipment losses.

2. Run time

Unplanned downtime comes out of planned production time. This gives the time the machine was actually running.

3. Availability

4. Performance

The ideal time for 766 parts is 383 minutes. That matches run time exactly, so performance is 100.0%.

5. Quality

6. OEE

This shift finished at 85.1% OEE. That is a strong number, but the loss split still matters: downtime cost 47 minutes, and quality cost 34 parts.

What good looks like

A common benchmark is 85% world-class for discrete manufacturing. Around 60% is typical for many plants starting a serious improvement effort. Do not use either number as a club. Use OEE to pick the next problem to attack and to prove whether the countermeasure worked.

Three common OEE mistakes

1. Mixing planned and unplanned downtime. Breaks, meetings, and scheduled PM reduce planned production time. Breakdowns and waiting on material reduce run time.
2. Using actual cycle time instead of ideal cycle time. Performance must compare output to the best demonstrated or engineered ideal. If you use actual cycle time, you hide slow-running losses.
3. Averaging OEE across lines. A straight average can bury the constraint. Track each line separately, then roll up with the right weighting if management needs one plant number.