What Is System Availability?

September 28, 2022

System availability is a maintenance metric used to measure the amount of time—as a percentage—that an asset can be used for production. It calculates the probability that a system won’t experience downtime when workers need to use it. 

Also referred to as equipment or asset availability, this availability measure is an essential metric for organizations that depend on complex pieces of equipment to function.

Manufacturers, warehousers, and oil/gas providers are some of the providers most likely to track this key performance indicator (KPI). As mentioned before, the definition of availability calculates the probability that an asset will be available when needed for production. 

An asset must meet the following three qualifications to be considered “available”:

  1. Functionality:  It is not out-of-service for inspection or repair work. 
  2. Normalcy: It runs in an ideal setting at an expected rate.
  3. Availability: It is available for use without disrupting production schedules. 

In other words, system availability quantifies the probability that, for example, your most integral forklifts, conveyor belts, and HVAC units are in good working condition and are not prone to outages.

“World-class maintenance is not just about the maintenance practices of the maintenance organization in a vacuum. It is about the way the entire organization uses all the means at its disposal to protect its ability to produce exceptional value for its customers. It is a journey, not a destination—a process, not a product.”

Reliable Plant

How to Calculate System Availability

System availability is expressed as a percentage of the actual operation time divided by the total amount of observational time. In other words, it’s the total asset uptime divided by the sum of the total amount of uptime and downtime. Higher availability, which translates to lower failure rates, means fewer system failures and less corrective action.

System Availability Formula 

System availability = uptime / (uptime + downtime) * 100

Or, put another way,

System availability = (Actual operation time in hours / Total time in hours) * 100


A conveyor belt in a factory was observed for 10 hours in one day. During that time, it broke down and took two hours to repair. The system availability for the conveyor belt is:

(Actual operation time in hours / Total time in hours) * 100

(8 hours / 10 hours) × 100

System availability = 80%

While maintenance professionals most frequently use the above equation, some managers prefer to use other availability calculations. For example, an availability calculation can be measured in terms of nines. Five-9’s (availability percentage = 99.999%) means less than 5 minutes and 15 seconds a year when a piece of equipment may not operate correctly, and would therefore be unavailable. Higher availability percentages translate into a company’s total operational availability and service level.

Alternative Method to Calculate System Availability 

An alternative route is to use the maintenance metrics Mean Time Between Failure (MTBF) and Mean Time to Repair (MTTR) to arrive at your final calculation. 

Both MTBF and MTTR reveal the effects of breakdowns on asset operational times. MTBF describes the period when an asset is performing under good working conditions. MTTR, on the other hand, refers to the amount of time it takes to repair an asset. 

Use the following formula to calculate availability: 

System availability = MTBF / (MTBF + MTR)

Ultimately, the formula you use to measure system availability is a matter of personal preference.   

Why Tracking System Availability Matters

Maintenance managers rely on this availability to determine how effectively existing maintenance strategies, activities, and schedules are maintaining uptime. 

In addition, eliminating single points of failure in say, one piece of equipment, means that you have added “redundancy” into operations. Failure of that one piece of equipment does mean failure or downtime of the entire production line. Measuring the availability of a system translates directly into building system reliability.

The KPI helps organizations gauge how well they maintain their tangible assets necessary for meeting high production standards. For this reason, striving to maximize the availability of the system to safeguard company profitability. 

The amount of time a critical asset remains operational is directly proportional to facility output and performance. For example, automobile manufacturers lose an estimated $50,000 per minute, or $3 million per hour, to downtime. While most industries lose considerably less, averages still range tens of thousands of dollars per hour. 

Reliable Plant reports that experts consider “world-class system availability” to be a minimum of 90 percent. 

System Availability vs. Asset Reliability 

It’s worth mentioning that the terms system availability and asset reliability are often mistakenly used interchangeably. System availability is impacted by both planned and unplanned downtimes. However, asset reliability refers to the probability of an asset performing without failure under normal operating conditions for a given period—it’s the absence of unplanned downtimes.

For example, an asset that never experiences unplanned downtime is 100 percent reliable but only 90 percent available. Why? Because it’s shut down once every 10 hours for routine maintenance. With that said, increased reliability translates to increased availability. 

On the flip side, increased unavailability means that the period of time equipment and systems are down is potentially eating into your company’s efficiency, effectiveness, and profits. It may even be time for a new system design or to check in with a reliability engineering team.

Another factor that impacts asset availability is maintainability. Maintainability refers to how quickly technicians detect, locate, and restore asset functionality after downtime—the higher the maintainability, the higher the availability. This characteristic is commonly measured using a KPI called Mean-Time-to-Repair (MTTR). MTTR represents the average time needed to repair a malfunction on a particular asset.

How Is System Availability Used in Maintenance? 

Maintenance management methods, standard operating procedures (SOPs), and maintenance tools all influence system availability. 

System availability as a maintenance metric is used to measure how effective existing maintenance systems are and to improve them. Whether planned or unplanned, equipment downtime has the biggest impact on system availability. 

Common causes of unplanned downtime include lack of proactive maintenance, aging equipment, mechanical failures, and operator errors. Thus, maintenance teams must work together to identify root causes of routine equipment failures instead of constantly performing “bandage” maintenance jobs. 

3 Ways to Improve System Availability 

As previously mentioned, the more uptime your team experiences, the better your company’s bottom line. Here are three simple ways to improve system availability:

1. Optimize Your Preventive Maintenance Program

Preventive maintenance helps to minimize asset failure and the need to take pieces of equipment out of production. Optimize PM processes by identifying which PM tasks need priority and how often they should be performed to help to maximize asset availability. Read What Is Preventive Maintenance? The Beginner’s Guide to Running PMs to learn more. 

2. Use Short Codes

Use a CMMS platform like MaintainX to catalog work orders with failure codes, cause codes, and remedy codes. Each abbreviation code should describe a typical equipment issue, cause of failure, and remedy. For example, you might describe an air leak as ARLK.  

Failure codes ensure all team members are on the same page when documenting both equipment issues and resolutions in data management platforms. This maintenance management hack supports accurate reporting data to draw from when conducting a Failure Mode and Effects Analysis (FMEA) or Root Cause Analysis. 

When sorting through a filtered short-code search for ARLK, for example, managers can easily see which assets have broken down because of an air leak. Organizations can develop specific codes, but those with stringent tracking requirements should consult standardized codes generated by regulatory bodies. 

3. Streamline SOPs

SOP checklists, workflows, and work instructions support technicians in performing tasks as efficiently as possible. When easily accessible and clearly written, SOPs help minimize human error, reduce excess spending, and increase machine availability. Read 8 Tips for Developing Standard Operating Procedures (That Get Used) to learn more. 


Increased system availability leads to improved efficiency, higher production levels, and healthier business margins. Put simply, the best way to improve availability is to reduce downtime! Promote a company culture where everyone understands the impact of reduced downtime on company productivity, customer service, and profit margins. Furthermore, implement user-friendly software, like MaintainX, to streamline worker communication and provide real-time data input and metrics reporting.

system availability
Caroline Eisner
Caroline Eisner
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