90.0%
432 minutes runtime from 480 planned production minutes.
OEE CALCULATION
How is OEE calculated?
OEE combines three factors—Availability, Performance and Quality. The standard relationship is OEE = Availability × Performance × Quality.
THE OEE FORMULA
OEE = Availability × Performance × Quality.
Each component is expressed as a percentage, converted to a decimal and multiplied. For example, 90% Availability × 95% Performance × 99% Quality equals 84.6% OEE.
The multiplication is important because losses compound. A machine can look strong in each individual component and still produce a noticeably lower overall OEE result.
1. Calculate Availability
A common Availability formula is Runtime ÷ Planned Production Time. If a machine is planned to run for 480 minutes and records 432 minutes of runtime, Availability is 432 ÷ 480 = 90%.
The difficult part is defining planned production time consistently. Decide how scheduled breaks, planned maintenance, changeovers and other planned stops are treated before comparing machines or sites.
2. Calculate Performance
Performance compares actual production with the amount expected at the defined ideal or target rate. If the machine could produce 1,000 units during its runtime at the agreed rate but produces 950 units, Performance is 95%.
A target that is obsolete or physically unrealistic can distort OEE. Product mix matters too: the correct rate for one SKU may be different from another.
3. Calculate Quality
Quality is commonly Good Output ÷ Total Output. If 950 units were produced and 940 were good, Quality is approximately 98.9%.
Define when rejects, rework and scrap are counted. If quality information is entered later than the production count, the current-shift OEE result may change as the data catches up.
WORKED EXAMPLE
Putting the three components together.
Assume a production line records 90.0% Availability, 95.0% Performance and 99.0% Quality. Convert the percentages to decimals and multiply:
95.0%
950 units produced compared with 1,000 expected at the agreed rate.
99.0%
Approximately 99% of total output is accepted as good production.
OEE = 0.90 × 0.95 × 0.99 = 0.846, or 84.6%. The next useful step is not simply to celebrate or criticise 84.6%; it is to look at which component and underlying events are creating the biggest recoverable loss.
DATA QUALITY
Common reasons OEE calculations become misleading.
Inconsistent planned-time rules
Different treatment of breaks, maintenance or changeovers can make two otherwise similar OEE results impossible to compare fairly.
Incorrect ideal cycle or target
Performance can exceed 100% or look artificially weak when the target rate does not represent the product and machine actually running.
Bad counts or delayed quality data
Duplicate pulses, counter resets, missing rejects or unit-conversion errors can create a precise-looking number that does not match the floor.
COMMON QUESTIONS
Frequently asked questions.
Why do OEE calculations differ between factories?
Plants can define planned time, ideal rate and quality rules differently. Clear definitions are important when comparing results.
Can OEE exceed 100%?
A sustained result above 100% usually indicates that the target or ideal rate, unit conversion or data definition should be reviewed.
EXPLORE MORE
Related ClearRivet information.
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