Availability

Availability is a performance metric that describes the proportion of planned time that an asset, process, or system is in a state where it can perform its intended function. In industrial operations, it is most often applied to production equipment, automated lines, utilities, or OT/IT systems that support manufacturing.

In mathematical form, availability is commonly expressed as:

Availability = (Run Time) / (Planned Production Time)

Where:

• Planned production time excludes scheduled shutdowns such as holidays or planned long-term outages, but usually includes normal shifts and planned operating windows.
• Run time is the portion of that planned time where the equipment or system is actually operating and capable of producing, excluding downtime events.

Availability in OEE and manufacturing metrics

Within Overall Equipment Effectiveness (OEE), availability is one of the three standard components, alongside performance and quality. In that context, availability measures production losses caused by events such as:

• Unplanned equipment failures or breakdowns
• Unscheduled maintenance or repairs during planned production time
• Changeovers and setups, when considered as downtime
• Regulatory or quality holds that stop the line
• Material shortages that halt production, when tracked as equipment downtime

On manufacturing shop floors, availability is typically tracked in MES, historian, or equipment monitoring systems using signals such as machine states, run/idle/stop codes, or work-center status in ERP/MES. In regulated environments, downtime reasons are often coded in detail to support root-cause analysis, change control, and auditability.

System and OT/IT availability

Outside of the OEE context, availability also describes how often an information system, network, or service is accessible and functioning as required. In OT and IT for manufacturing, this may refer to:

• Availability of an MES, historian, LIMS, or QMS application
• Availability of control systems, PLCs, SCADA, or data collection interfaces
• Network or data center uptime that supports production and compliance activities

In this systems context, availability is often expressed as a percentage of total calendar time (for example, a target of 99.5% system uptime over a month), including both planned and unplanned outages, depending on the defined service level.

What availability includes and excludes

• Includes: Time when the asset or system is ready and able to perform its intended function, regardless of actual demand or loading.
• Usually excludes: Clearly defined, scheduled downtime such as long-term planned shutdowns or off-shift periods, depending on the agreed measurement definition.
• Does not directly measure: Production speed, yield, or quality; those are captured separately by performance and quality metrics.

Common confusion

• Availability vs. reliability: Reliability focuses on the likelihood that an asset will perform without failure over a time interval. Availability focuses on how much time an asset is up and ready, which can be influenced by both reliability and maintainability.
• Availability vs. utilization: Utilization tracks how much of the available time is actually used for production, considering demand and scheduling. Availability only reflects whether the equipment or system could run if needed.
• Availability vs. uptime: Uptime is sometimes used informally as a synonym, but availability usually has a clearer, agreed definition relative to planned or calendar time.

Tie to acceptable OEE context

When discussing an acceptable OEE value, availability is one of the key components that can vary widely by product mix, equipment age, validation constraints, and change-control practices. Because definitions of planned time and downtime categories differ by site, availability values are only comparable when measurement rules and data collection methods are clearly defined and consistently applied.