Guide · OEE

How to calculate OEE for a CNC job shop (with a free calculator)

One formula, three numbers you already have at the end of a shift, and a worked example on a turning centre. Plus the four mistakes that make OEE look better than it is.

Updated · By the OpeEye team, Rajkot

Short answer

OEE = Availability × Performance × Quality. Availability is run time divided by planned production time; Performance is ideal cycle time × pieces made, divided by run time; Quality is good pieces divided by total pieces. For a shift with 450 planned minutes, 62 minutes of stops, a 48-second cycle, 410 pieces and 9 rejects, OEE is 86.2% × 84.5% × 97.8% = 71.2%.

OEE calculator

Type your shift's numbers. The defaults are the worked example below.

Your OEE

71.3%

Typical for a shop that measures. The gap to 85% is the hidden factory.

Availability
86.2%
388 of 450 min running
Performance
84.5%
410 of 485 possible pcs
Quality
97.8%
401 of 410 good

Downtime alone cost about 77 pieces this shift at the ideal cycle.

The five numbers you need from the floor

Inputs

Planned production time
Shift length minus planned breaks (min)
Downtime
Every unplanned stop: setup, breakdown, tooling, waiting (min)
Ideal cycle time
Fastest repeatable time per piece (sec) — from the part master
Total pieces
Good and rejected, counted at the machine
Rejected pieces
Scrap and rework

Step by step

  1. 01

    Availability

    Run time = planned time − downtime. Availability = run time ÷ planned time.
    450 − 62 = 388 min. 388 ÷ 450 = 86.2%.
  2. 02

    Performance

    Ideal output = run time ÷ ideal cycle. Performance = actual ÷ ideal.
    388 × 60 ÷ 48 = 485 pcs possible; 410 ÷ 485 = 84.5%.
  3. 03

    Quality

    Good pieces ÷ total pieces.
    (410 − 9) ÷ 410 = 97.8%. OEE = 0.862 × 0.845 × 0.978 = 71.2%.

What is a good OEE?

The benchmark most people quote comes from OEE.com: 85% is world-class for discrete manufacturing, 60% is typical, and 40% is common for plants measuring for the first time. World-class is usually quoted as 90% availability × 95% performance × 99.9% quality.

Job shops sit lower than high-volume lines by nature — more setups, more part changes — so compare a machine with itself over time, not with a benchmark from a bottling plant. The useful question is not “is 71% good?” but “which of the three factors is costing the most, and what is the biggest reason inside it?”

Four mistakes that make OEE look better than it is

Common OEE calculation mistakes
MistakeWhat it doesDo this instead
Using average cycle time as the idealPerformance reads ~100% by definitionUse the part master's ideal cycle or a timed best run
Not logging stops under 10 minutesAvailability is inflated; the loss hides in performanceLog every stop at the moment, one tap, with a reason
Counting setup as run timeAvailability looks fine; setups never get shorterSetup is downtime; track it separately too
Counting rejects at inspection, not at the machineQuality is right, but the cause and the time are lostLog rejects at the machine with a reason

OEE per job, not just per machine

A machine's OEE mixes every part it ran. The number that changes quoting is OEE per part: which components run near their ideal cycle with few rejects, and which ones quietly lose money on every batch. You get that only when each piece, stop and reject is attached to a job card — the reason production tracking and OEE belong on the same screen.

Skip the spreadsheet. See your real OEE by the end of the first shift.

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Questions shop owners ask

What is the OEE formula?

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OEE = Availability × Performance × Quality. Availability = run time ÷ planned production time. Performance = (ideal cycle time × total pieces) ÷ run time. Quality = good pieces ÷ total pieces. Multiply the three as decimals; the result is your OEE as a percentage.

What counts as planned production time?

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The shift length minus planned breaks — tea, lunch, planned maintenance, and any time the machine was not scheduled to run. Everything else that stopped the machine is downtime and counts against availability.

Where do I get the ideal cycle time?

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From the part master or a timed run of the fastest repeatable cycle — the time the process allows, not the average you usually get. Using the average instead of the ideal is the most common way OEE gets flattered.

Is setup time downtime?

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Yes — in standard OEE, changeover and setup count as availability loss because the machine is not producing. Many job shops track setup separately as well, because it is the loss they can do most about.

Should rework count as a reject?

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Yes. Quality counts pieces that were right the first time. A reworked piece was not, so it is a quality loss even if it eventually ships.

How is OEE different from utilisation?

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Utilisation asks how much of the calendar the machine ran. OEE asks how well it produced when it was planned to run, including speed and quality. A machine can have high utilisation and poor OEE — running all day at half speed, making scrap.

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