Reliability and uptime
Equipment downtime calculator
Downtime percentage is the share of a period the asset was unavailable. It is the simplest reliability figure to produce and the easiest to argue about, because everything depends on which hours you put in the denominator.
Downtime % = Downtime hours ÷ Total hours in period × 100
Calendar hours, or scheduled hours. Be consistent and say which
Show the assumptions
- Formula
- Downtime % = Downtime hours ÷ Total hours in period × 100
Pick one denominator and keep it. Switching between calendar hours and scheduled hours between reports is the fastest way to make a genuine improvement look like a regression.
Downtime percentage
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Prefilled with an example. Change any number and the result updates.
How to calculate Downtime percentage
Downtime % = Downtime hours ÷ Total hours in period × 100
Worked example
- Downtime hours 24 hrs
- Total hours in period 720 hrs
Downtime percentage = 3.33%
Reading the result
Pick one denominator and keep it. Switching between calendar hours and scheduled hours between reports is the fastest way to make a genuine improvement look like a regression.
Downtime percentage questions
Should I use calendar hours or scheduled hours?
Scheduled hours answer "how much of the time we needed it, did we have it", which is usually the operational question. Calendar hours answer "how much of the time did we own an asset that could not run", which is the capital question. Both are legitimate. Reporting one and labelling it the other is not.
Does planned maintenance count as downtime here?
In this calculation, yes, if it falls inside the period you are measuring. That is the difference between this figure and OEE availability, which removes planned maintenance from the denominator entirely.
Related calculators
See downtime trends
UpKeep records the work, the hours and the failures this metric depends on, so Downtime percentage is a report rather than a spreadsheet exercise.