OEE (Overall Equipment Effectiveness) for SMEs

OEE — Overall Equipment Effectiveness — is probably the most useful production metric ever devised. It distils plant performance into a single number and, more importantly, splits that number into three components that point directly at what to improve. Often associated with big factories, OEE is genuinely useful even in a small workshop with a handful of machines. Here is the working understanding.

The formula

OEE has a simple multiplicative structure:

OEE = Availability × Performance × Quality

Each component is a ratio between 0 and 1 (or 0–100%):

• Availability = how often the equipment was running when it was scheduled to run
• Performance = how fast it ran compared to its ideal speed
• Quality = how many of the units it made were good (vs scrap / rework)

A machine that was available 90%, ran at 95% of its rated speed, and produced 98% good units has OEE of 0.90 × 0.95 × 0.98 = 83.8%.

Why multiplicative

The components multiply because each one represents a "tax" on the previous one. A machine that's available a lot but slow doesn't produce a lot. A fast machine that breaks frequently doesn't either. A machine that produces fast but produces scrap also doesn't produce useful output.

Each component covers a separate loss type, and they compound.

Availability — the time lost

Availability = Run Time ÷ Planned Production Time

Where:

• Planned Production Time = the time the equipment was scheduled to be running (typically shift hours minus planned breaks)
• Run Time = Planned Production Time minus unplanned stops (breakdowns, changeovers running over, material starvation)

Common availability losses:

• Breakdowns — equipment failure, repair time
• Setup / changeover — too long, too often
• Minor stops and starts — quick adjustments that add up
• Material starvation — waiting for upstream
• Operator absence — gap in coverage

A typical SME with no measurement starts around 60-70% availability — most of the loss invisible because it's not tracked.

Performance — the speed lost

Performance = (Ideal Cycle Time × Total Units Produced) ÷ Run Time

In English: of the time you were actually running, how close were you to the ideal speed?

Common performance losses:

• Reduced speed — running slower than rated (often deliberate, sometimes due to wear)
• Minor stops — sub-minute stops not counted as breakdowns
• Idling — equipment running without producing

Performance loss is the most invisible component because it doesn't show as downtime — the machine is running, just not producing what it should.

Quality — the units lost

Quality = Good Units ÷ Total Units Produced

The cleanest of the three to measure. Rework counts as a quality loss (the unit wasn't right first time, even if eventually saved). Scrap counts as a complete loss.

Common quality losses:

• Process defects — caught during production
• Start-up / warm-up rejects — first units of a run often not right
• Rework rate — units fixed rather than first-pass good

See our scrap and yield post for the accounting side of these.

A worked example

A small workshop, one CNC machine:

• Scheduled to run 8 hours per shift × 1 shift = 480 minutes/day
• Planned breaks: 30 minutes. Planned Production Time = 450 minutes
• Actual running time: 380 minutes (unplanned stops + breakdowns + setup overruns took 70 min). Availability = 380/450 = 84.4%
• Ideal cycle time: 6 minutes/unit. Units produced: 50. Run-time-equivalent at ideal speed: 50 × 6 = 300 minutes. Performance = 300/380 = 78.9%
• Of 50 units produced, 47 good, 3 scrap. Quality = 47/50 = 94%

OEE = 0.844 × 0.789 × 0.94 = 62.6%

A 62.6% OEE is roughly typical for an unmeasured operation. World-class is considered 85% — meaning 99% availability, 95% performance, 99% quality.

Why this decomposition is powerful

The single OEE number tells you you have a problem. The decomposition tells you what kind of problem:

• Low availability — focus on reducing downtime: faster changeovers, better preventive maintenance, ensuring upstream material is ready
• Low performance — focus on cycle-time discipline: running at rated speed, eliminating minor stops, operator training
• Low quality — focus on first-time-right: better process control, tooling condition, operator training, in-line inspection

A workshop with 90% availability, 90% performance and 60% quality has a very different action list than one with 60% availability, 90% performance and 90% quality. The decomposition forces the right conversation.

How to start measuring in a small workshop

For SMEs without sensors and automated logging, a simple manual approach:

• A shift log per machine: start of shift, planned production time
• Operator logs every downtime event > 5 minutes (with cause)
• Output is counted per shift (units produced, good, scrap)
• A daily OEE calculation per machine (15 minutes of analysis)

The exact number is less important than the trend — week-over-week improvement is the goal. The discipline of measuring drives improvement even without sophisticated tools.

OEE vs utilisation

A common confusion: OEE is not the same as utilisation. Utilisation usually means "% of available time the machine ran" — closer to Availability alone, missing the performance and quality dimensions.

A machine can be at 100% utilisation (running all the time) but at 50% OEE because it's running slow and producing scrap. Utilisation feels good; OEE tells the truth.

What OEE doesn't tell you

OEE measures the equipment, not the business case. A machine making things nobody wants at 100% OEE is still a problem. Pair OEE with:

• Demand / order book — is production matching demand?
• Margin per unit — is the output profitable?
• Capacity vs need — do we have too much / too little capacity?

OEE is the operational lens; the commercial lens has to sit alongside it.

How Booksmor helps

Booksmor's production module captures downtime, run-time, cycle time and quality data from every production run — and computes OEE per machine, per shift, per product. Trends and component decomposition are visible at a glance; consistent OEE shortfalls flag for action. Start a 30-day free trial and put your equipment performance on a real footing.