OEE (Overall Equipment Effectiveness) is a single number that says what share of the planned time the machine actually spent making good parts at the specified speed. 100% means: no downtime, no slowdowns, no scrap.
The formula
OEE is the product of three parts:
- Availability = run time ÷ planned time. Reduced by downtime: breakdowns, setup, waiting for material.
- Performance = (parts made × ideal cycle time) ÷ run time. Reduced by slow cycles and short stops that nobody writes down.
- Quality = good parts ÷ parts made. Reduced by scrap and rework.
OEE = availability × performance × quality.
A shop-floor example
An 8-hour shift with a 30-minute break → planned time 450 min. The machine was down for 45 min (a breakdown and a tool change) → it ran for 405 min. Availability = 405 ÷ 450 = 90%.
The ideal cycle time is 30 s and 730 parts were made. 730 × 0.5 min = 365 min of “pure” running out of 405 → performance = 90%.
Of the 730 parts, 22 are scrap → quality = 708 ÷ 730 = 97%.
OEE = 0.90 × 0.90 × 0.97 = 78.6%. Each part looks fine on its own, but together more than a fifth of the shift is lost.
How good is good?
85% is often cited as world class (90% × 95% × 99.9%). Many plants that measure accurately for the first time see 40–60%. That is not bad news — it is the first true picture. What matters is that the trend goes up and that you know where the minutes go.
What is not part of OEE
Breaks, meetings and planned maintenance are outside the planned time, so they do not lower OEE. If planned maintenance runs longer than the plan, the excess is already a loss of availability.
Most common mistakes
- Downtime is written down at the end of the shift — from memory. Short stops vanish and long ones get “rounded”.
- Performance is calculated with the actual cycle time instead of the ideal one — then a slow machine looks perfect.
- One number for the whole factory — OEE makes sense per machine and per shift; the total hides the problems.
In MachineTakt
Downtime is recorded automatically from the machine’s pulse, and the operator codes the reason on a tablet with two taps. OEE and its three parts are visible live by machine, line and shift, together with the Pareto of losses. To see how much you are losing, try the OEE calculator.