How to Calculate OEE (and Why Your Factory is Losing 20% Throughput)

Most factory managers know their machines are running. What they don’t know is how well they’re running — and the gap between those two things is usually 20–30% of production capacity sitting quietly on the floor, unaccounted for.

OEE (Overall Equipment Effectiveness) is the standard metric for finding that gap. This guide explains the formula, walks through a real calculation, shows you what a good score looks like by industry, and explains what to do once you have a number.

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What Is OEE?

OEE stands for Overall Equipment Effectiveness. It measures what percentage of planned production time is truly productive — meaning the machine was running, running at full speed, and producing good parts.

It was developed as part of Total Productive Maintenance (TPM) in Japan in the 1960s and is now the global standard for manufacturing efficiency measurement.

If you’re new to how production software tracks this, read our plain-English MES guide first.

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The OEE Formula

OEE is the product of three factors:

OEE = Availability × Performance × Quality

Each factor sits between 0% and 100%. A perfect score — 100% OEE — means the machine ran continuously, at full rated speed, with zero defects. In practice, world-class manufacturers target 85% OEE. Most factories start somewhere between 55–65%.

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Step-by-Step: How to Calculate OEE

Step 1 — Calculate Availability

Availability measures how much of the planned production time the machine was actually running.

Availability = Run Time ÷ Planned Production Time

Run Time = Planned Production Time − Downtime
Downtime includes: breakdowns, changeovers, planned maintenance, material shortages, waiting for operators.

Example:

• Shift length: 8 hours (480 minutes)
• Scheduled breaks: 30 minutes
• Planned Production Time: 450 minutes
• Unplanned downtime (breakdown + changeover): 60 minutes
• Run Time: 390 minutes

Availability = 390 ÷ 450 = 86.7%

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Step 2 — Calculate Performance

Performance measures whether the machine ran at its full rated speed when it was running.

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

Ideal Cycle Time = the fastest time the machine can produce one part (from the manufacturer spec or your best historical result).
Total Count = all parts produced in Run Time (good + defective).

Example:

• Ideal Cycle Time: 1.0 minutes per part
• Run Time: 390 minutes
• Parts produced: 351 (includes defective)

Performance = (1.0 × 351) ÷ 390 = 90.0%

Performance losses include micro-stops, slow cycles, and reduced speed from worn tooling or incorrect settings.

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Step 3 — Calculate Quality

Quality measures what fraction of parts produced were good on the first pass.

Quality = Good Count ÷ Total Count

Good Count = Total Count − Defective Count (rejects + rework)

Example:

• Total Count: 351
• Defects: 18
• Good Count: 333

Quality = 333 ÷ 351 = 94.9%

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Step 4 — Calculate OEE

Multiply all three:

OEE = 86.7% × 90.0% × 94.9% = 74.0%

This machine is running at 74% OEE — meaning 26% of its planned production time is being wasted through downtime, slow cycles, and defects.

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OEE Calculation — Visual Flow

flowchart TD
  A["Planned Production Time (450 min)"] --> B["minus Downtime (60 min)"]
  B --> C["Run Time (390 min)"]
  C --> D["Availability = 390 / 450 = 86.7%"]
  C --> E["Parts Produced (351)"]
  E --> F["Performance = 351 / 390 = 90.0%"]
  E --> G["minus Defects (18)"]
  G --> H["Good Count (333)"]
  H --> I["Quality = 333 / 351 = 94.9%"]
  D --> J["OEE = 86.7% x 90.0% x 94.9% = 74.0%"]
  F --> J
  I --> J

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What Is a Good OEE Score?

OEE Score	Rating	What It Means
< 50%	Poor	Significant losses; urgent intervention needed
50–65%	Average	Typical of factories not actively measuring OEE
65–75%	Good	Above average; targeted improvement underway
75–85%	Excellent	World-class for high-mix/low-volume environments
> 85%	World Class	Benchmark for high-volume, dedicated lines

Industry benchmarks (approximate):

Industry	Typical OEE Range
Automotive (mass production)	80–90%
Semiconductor / Electronics	70–80%
Metal Fabrication / Grinding	55–70%
Food & Beverage	60–75%
Plastics / Injection Molding	65–75%

Most factories in Thailand and Southeast Asia that are measuring for the first time land at 55–65%. That’s not unusual — it’s just the starting point.

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The Six Big Losses Behind Low OEE

OEE was designed to expose the Six Big Losses defined in TPM. Every OEE gap traces back to one of these:

Loss Category	Factor Affected	Example
Breakdowns	Availability	CNC spindle failure
Setup and Adjustments	Availability	Die changeover, first-piece inspection
Small Stops	Performance	Jammed feeder, misaligned sensor trigger
Reduced Speed	Performance	Running at 80% to avoid vibration
Production Defects	Quality	Out-of-spec parts during steady state
Startup Defects	Quality	Scrap during warm-up after changeover

flowchart TD
  A["Six Big Losses"] --> B["Availability Losses"]
  A --> C["Performance Losses"]
  A --> D["Quality Losses"]
  B --> E["Breakdowns"]
  B --> F["Setup and Adjustments"]
  C --> G["Small Stops"]
  C --> H["Reduced Speed"]
  D --> I["Production Defects"]
  D --> J["Startup Defects"]

When you see OEE at 74%, the three-factor breakdown (Availability 86.7% / Performance 90% / Quality 94.9%) immediately tells you where to focus. In this example, Availability is the biggest problem — investigate downtime root causes first.

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How to Track OEE in Practice

Option 1: Manual / Spreadsheet

Operators record start/stop times, part counts, and defects on paper or Excel. Works for 1–3 machines. Data quality degrades fast at scale and shift handover gaps are common.

Option 2: SCADA / PLC Signal Integration

Automatic signal capture from PLC (machine ON/OFF, cycle count). Accurate downtime data; requires electrical integration. No context capture (the system knows the machine stopped, but not why).

Option 3: MES with OEE Module

An MES (Manufacturing Execution System) combines signal capture with operator-entered reason codes, work order context, and product-level quality data. This gives you OEE at line, shift, product, and operator level — and historical trend reporting.

simpliFactory captures OEE at the machine level with real-time dashboards and shift-by-shift trend reports. If you want to see what this looks like for your environment, send us a message →

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From OEE Number to Action

Measuring OEE is step one. The goal is to move it. Here’s a practical sequence:

flowchart TD
  A["Measure OEE baseline (2-4 weeks)"] --> B["Identify worst-performing machine"]
  B --> C["Break down by Availability / Performance / Quality"]
  C --> D{"Which factor is lowest?"}
  D --> E["Availability low: attack downtime root causes (PM, spare parts)"]
  D --> F["Performance low: check speed settings, micro-stop triggers"]
  D --> G["Quality low: review SOP, tooling wear, incoming material"]
  E --> H["Re-measure after 4 weeks"]
  F --> H
  G --> H
  H --> I["Move to next machine or next loss category"]

A 5-point OEE improvement on a single machine typically recovers 10–15% additional throughput — without adding headcount or capital equipment.

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FAQ

What does OEE stand for?
Overall Equipment Effectiveness. It measures the percentage of planned production time that is truly productive, combining Availability, Performance, and Quality into a single score.

What is a good OEE score?
85% is considered world class for high-volume manufacturing. Most factories measuring for the first time score between 55–65%. A score above 75% is excellent for high-mix environments like precision parts or job shops.

What is the OEE formula?
OEE = Availability × Performance × Quality. Availability is run time divided by planned time. Performance is actual output rate versus ideal rate. Quality is good parts divided by total parts produced.

What causes low OEE?
The Six Big Losses: breakdowns and changeovers (hit Availability); micro-stops and reduced speed (hit Performance); production and startup defects (hit Quality). Most factories have the most room to gain in one specific category — OEE’s three-factor structure tells you which one.

How do I track OEE without expensive software?
Start with a paper log or Excel template. Record planned time, downtime start/end with reason, total parts, and defective parts per shift. Manual tracking is sufficient for a baseline on 1–3 machines. As you scale to 5+ machines or want real-time visibility, an MES with OEE integration becomes practical.

Can OEE be above 100%?
Technically yes — if your Ideal Cycle Time is set slower than the machine’s true maximum speed. This signals a miscalibrated standard, not a genuine achievement. Review your Ideal Cycle Time baseline.

How is OEE different from utilization?
Utilization only measures whether the machine was running. OEE adds speed and quality — a machine running at 60% of rated speed with 10% defect rate has high utilization but low OEE.

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→ What is a Manufacturing Execution System? A Plain-English Guide

Questions about OEE tracking for your factory?
Talk to the simpliFactory team → hello@simplico.net