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Production & Lean

OEE Calculation Guide

Overall Equipment Effectiveness (OEE) shows how much of a machine's planned time is actually producing good parts at the right speed. This guide explains the formula with a worked example.

By Career Plus Academy — manufacturing career development for Production and Quality professionals in India.

What it means

OEE = Availability × Performance × Quality. Availability covers stoppages, Performance covers speed loss and minor stops, and Quality covers rejects and rework.

Why it matters in manufacturing

OEE breaks one vague problem — "the line is not producing enough" — into three specific loss areas, so the team knows where to focus.

Calculating OEE step by step

  1. 1

    Planned production time

    Shift time minus planned breaks, e.g. 480 − 60 = 420 minutes.

  2. 2

    Availability

    Run time ÷ planned production time. With 60 minutes of breakdowns and changeovers: 360 ÷ 420 = 85.7%.

  3. 3

    Performance

    (Ideal cycle time × total count) ÷ run time. Ideal cycle 1 minute, 300 parts: 300 ÷ 360 = 83.3%.

  4. 4

    Quality

    Good count ÷ total count. 285 good of 300: 95.0%.

  5. 5

    OEE

    Use unrounded factors: (360 ÷ 420) × (300 ÷ 360) × (285 ÷ 300) = 67.86%, or 67.9% to one decimal place. Cross-check: 285 good parts × 1 minute ÷ 420 planned minutes.

  6. 6

    Act on the biggest loss

    Use loss data (breakdowns, changeovers, minor stops, speed loss, start-up rejects, process rejects) to target improvement.

Practical shop-floor example

Illustrative learning example — not a client result

Example: CNC cell

A CNC cell shows good availability but low performance. Observation reveals frequent short stops for chip clearing that were never recorded as downtime. A coolant nozzle change reduces the stops and performance improves without extra investment.

Common mistakes

  • Using a faster-than-real ideal cycle time, or a slower one to look good.
  • Hiding changeover time as planned downtime.
  • Counting reworked parts as good first-time parts.
  • Comparing OEE between very different machines.

Practical checklist

  • Planned time defined consistently
  • Ideal cycle time agreed and documented
  • Downtime reasons recorded
  • Good count excludes rework
  • Losses reviewed daily
  • Actions tracked against the biggest loss

Frequently asked questions

What is a good OEE?

It depends on the process and industry. Focus on your own trend and the biggest losses rather than a universal benchmark.

What is the difference between OEE and TEEP?

OEE is based on planned production time. TEEP is based on all calendar time, including unplanned shifts.

Does changeover time reduce Availability?

Yes, when it occurs within planned production time. Define planned production time consistently; do not exclude changeovers simply to increase reported OEE.

Why is my Performance above 100%?

Check the ideal cycle time, counts, time units and run-time records. Performance above 100% usually signals inconsistent inputs; investigate rather than just capping the number.

Can I count reworked parts as good parts?

Use first-pass good count for OEE Quality. Reworked parts are a quality loss even if later acceptable. Keep the counting rule consistent.

References and further reading

This introductory guide does not replace applicable manuals, customer requirements or approved safety and operating procedures.

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