This article is for plant managers, production managers, plant controllers and maintenance and continuous improvement leads who want a downtime cost figure they can defend. It deals with the factor many calculations estimate instead of measuring: the downtime hours themselves. Where do they come from, how do you measure the duration and frequency of stops, short stops included, and what changes in the calculation once those hours are measured?
- Downtime cost is an hourly rate multiplied by downtime hours.
- Those hours are often estimated, and short stops are usually missing.
- Measure duration and frequency separately, restarts included.
- Measure first, value second: the countermeasure then fits the pattern.
What LEMCON TECH writes about downtime cost
Jörg Lemmerer of LEMCON TECH, an engineering office for occupational safety, engineering and data analysis based in Bad Ischl, Austria, published Stillstandskosten realistisch berechnen: was ein Anlagenausfall wirklich kostet (“Calculating downtime cost realistically: what an equipment failure really costs”) on 29 October 2026. Starting from an analogy with the follow-on costs of workplace accidents, he shows what an equipment failure actually costs and why that cost is underestimated. He names the core problem plainly: “Der typische Mangel liegt darin, dass Betriebe Stillstandskosten meist aus der Produktionsplanung ableiten, nicht aus einer eigenen Kostenrechnung.” (The typical shortcoming is that companies mostly derive downtime costs from production planning, not from a cost calculation of their own.)
LEMCON TECH suggests recording four cost blocks per hour of downtime: labour costs, energy and operating costs, lost contribution margin, and the often overlooked restart costs. That sets up the first half of the calculation: the cost per hour. This article adds the second half: how many hours does a machine really stand still, how often, and for how long each time? A downtime cost calculation is only as reliable as the hours it is multiplied by.
Where downtime hours come from in practice
Ask in a plant how many hours a machine was down last month, and the answer usually comes from one of three sources. Each has its blind spots.
- The shift log. Operators write breakdowns down by hand. Long failures are there, often with a rounded duration. Stops of a few minutes are rarely logged, because there is no time or because they feel normal.
- ERP or planning confirmations. They show the gap between planned and reported quantities. You can infer lost time from it, but not whether it came from one long failure, from many short stops or from a slower cycle.
- Memory. Meetings remember the dramatic failures. The daily small stuff disappears, even though it can add up to a lot of time over a month.
This is where LEMCON TECH’s observation meets shop floor experience: if you derive downtime costs from planning, you usually take the hours from planning too, and those hours are an estimate.
Duration and frequency: two quantities to measure separately
Downtime hours are the number of stops multiplied by their average duration. Two machines with the same total downtime can still behave very differently. For example, machine A stops a few times a month, for several hours each time. Machine B stops very often, for a minute or two each time. The total can be identical; the costs and the right countermeasures are not.
| Type of stop | Typical pattern | How it is usually recorded | Cost blocks most affected |
|---|---|---|---|
| Long failure (breakdown, tool breakage) | Rare, long duration | Shift log, maintenance work order | Lost contribution margin, restart costs |
| Medium stop (material shortage, waiting for release) | Regular, a few minutes to an hour | Partly in the shift log, often without a reason | Labour, energy and operating costs |
| Short stop (jam, sensor fault, readjustment) | Very frequent, seconds to a few minutes | Barely or not at all | Labour, energy and operating costs, lost margin |
| Restart after a stop | After every longer stop | Rarely recorded separately | Restart costs |
Frequency is more than a side detail. Every stop carries a fixed share: the operator reacts, the alarm is acknowledged, the machine ramps back up. A machine that stops often therefore loses more than its downtime duration alone suggests. And because a restart follows every longer stop, the restart cost block that LEMCON TECH highlights depends directly on the number of events, not only on their duration.
Five steps to reliable downtime hours
- Define a stop clearly. When does the machine count as stopped: from the first missing cycle or only after a threshold? Set the threshold and write it down, otherwise months and machines cannot be compared.
- Capture every stop automatically, including short ones. Start, end and duration come from the machine signal, not from memory. This is the only way short stops show up in the figures at all.
- Assign reasons. The operator adds the reason at the line from a short list. Planned stops (breaks, maintenance, changeovers) are kept apart from unplanned ones, because they belong in a different calculation.
- Make the restart visible. The phase after a stop, when the machine runs slower or produces scrap, is shown as a separate segment. It is the quantity basis for restart costs.
- Analyse by duration and frequency, then put a price on it. Per machine and reason: count, total duration, average duration. Only then are the hours multiplied by the hourly cost rates.
The order matters: measure first, then value. Starting with the valuation means debating hourly rates while the biggest uncertainty sits in the hours.
What measured hours change in the decision
LEMCON TECH presents the downtime cost calculation as a basis for decisions, for instance on investing in redundancy, spare parts stock or preventive maintenance. Measured duration and frequency sharpen those decisions. A few long failures point towards spare parts, redundancy or a preventive strategy for the component involved. Many short stops point towards work on the cause at the line: feeding, settings, sensors, standard work. Without measurement both cases end up in the same total, and the chosen measure fits only by chance. Measured OEE shows both patterns side by side.
Measured hours also change unit cost calculations. We show how measured machine time affects them in Unit cost based on measured machine time. For a closer look at the small stops once they are measured, see Micro-stops: the invisible killer of your OEE.
How TEEPTRAK provides the hours
TEEPTRAK measures stops and short stops automatically and in real time. A module is wired into the electrical cabinet and a sensor is mounted at the line, with no connection to the PLC. Installation takes about one hour per machine, and OEE is available within 48 hours. Every stop is recorded with its start, end and duration, and operators assign the reason at the line. That produces the duration and frequency data a downtime cost calculation needs. TEEPTRAK is used in more than 700 plants in over 30 countries, where unplanned downtime falls by 30% on average.
Further reading
- LEMCON TECH: Stillstandskosten realistisch berechnen: was ein Anlagenausfall wirklich kostet
- Unit cost based on measured machine time
- Micro-stops: the invisible killer of your OEE
FAQ
Why is the downtime from the shift log not enough to calculate downtime cost? Because it usually captures long failures well but few short stops, and durations are often rounded. The hourly rates may be accurate, but the hours remain an estimate.
Should short stops be included in downtime cost? Yes. One short stop costs little, but together they can add up to many hours over a month. Because they are rarely recorded, they are often missing from the calculation entirely.
Why look at downtime duration and frequency separately? Because the same total hours can come from a few long stops or from many short ones. The cost structure, such as the restart for each event, and the right countermeasures differ considerably.
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