System Availability: Definition, How-To Guide and Example

By Indeed Editorial Team

Published September 29, 2021

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

Companies measure system availability to determine system productivity and efficiency. This performance metric also helps a company analyze the effectiveness of its current maintenance programs. Understanding the importance of system availability and how to calculate it can help you provide recommendations for improving your company's operations. In this article, we explore the concept of system availability, including its importance, its determining factors, how to calculate it and its use in an example.

What is system availability?

System availability is a performance metric that helps a company determine the likelihood that a system is available at a specific time instance. It analyzes the percentage of time a system is available for use, when it's down for a maintenance issue or when the system is actively undergoing maintenance. There are several classifications of availability which include:

• Instantaneous availability: This availability measures the probability a system or piece of equipment is ready for operation at a specific point in time.

• Average uptime availability: This metric represents the time a system is available for use over a specific period.

• Steady-state availability: Often referred to as long-term availability, this represents the availability of a system as a company analyzes an infinite amount of operating time.

• Inherent availability: This metric only measures the availability of a system by analyzing operating time and corrective maintenance and doesn't account for system standby or preventative maintenance measures.

• Achieved availability: This metric accounts for corrective and preventative maintenance when calculating system availability.

• Operational availability: This represents the proportion of time a system is operating or capable of operating.

Related: High-Availability Systems: Definition, Importance and Principles

Why is it important to measure system availability?

System availability is used to measure whether production potential is being maximized. Understanding this metric and knowing how to respond to it can directly affect a company's financial performance. Availability monitoring allows a company to:

• Observe these important metrics

• Detect issues proactively

• Identify improvement opportunities regarding machine or system maintenance

• Increase availability and create revenue opportunities

• Empower incident response teams with information and tools for managing incidents

• Measure and investigate the effectiveness of maintenance tools

What affects system availability?

Understanding how to improve system availability starts with knowing what factors increase or decrease the uptime or downtime of a system. Here are several components that can affect system availability:

• Preventative maintenance

• Broken machinery

• Maintenance processes

• Failure codes

Related: How To Optimize Maintenance Repairs and Operations Program

What is system reliability?

System reliability is another performance metric that helps a company determine the likelihood a system, including all hardware, firmware and software, meets performance standards during a specified time in a specified environment. It also measures the output yield and quality of the system. This metric can help a company identify improvement opportunities within its operations because it can highlight yield or quality concerns.

System availability vs. reliability

Although both concepts help a company improve its operations, these two performance metrics measure different aspects of a company's operations. System availability specifically measures how often a machine or piece of equipment is ready and available for use. Reliability specifically measures the output of a system by analyzing the quality and yield of a finished product.

Related: Measurement Validity vs. Reliability: What's the Difference?

How to calculate system availability

It's important to understand how to calculate system availability so you can improve your company's operations. Here's the formula to calculate system availability:

Percentage of availability = uptime / (uptime + downtime)

Here's a step-by-step guide to help you calculate system availability:

1. Determine the period you're going to analyze

The first step in calculating availability is deciding the period you want to analyze. Many companies analyze system availability on a daily, weekly, monthly or annual basis. This can help you discover system and maintenance trends.

2. Calculate your uptime hours

Once you've decided on the period you're measuring, you can calculate the total uptime hours for the system. These are the actual working hours of the system or machine, not counting the production time stopped for repairs or maintenance. For example, you may schedule a machine to operate seven hours each day, and you're choosing to analyze one workweek. You'd multiply seven by five, which results in 35. This shows the machine should be in operation for 35 hours during the week.

3. Discover total downtime hours

Downtime refers to the total time a machine's not in service. Maintenance, repairs or unexpected breaks are the usual downtime of a machine. It's important to only account for the amount of downtime that occurs during a system's scheduled operating hours. Logging machine downtime as it occurs can help you determine accurate downtime.

4. Add the total downtime to the uptime hours

This next step helps you discover the period a system could've been available for production. This figure gives you the maximum number of production hours that employees could use the system or machine. Companies use the result of this calculation in the final step of determining availability.

5. Make your final calculation

Once you get the result from the previous step, you can calculate the system availability percentage. To do this, divide your uptime hours by the result from the previous step. The result from this calculation is a decimal point. Multiply the result by 100 to discover the percentage of system availability.

6. Analyze results

Once you've determined availability for a period, you can analyze the results and implement improvement projects. Many companies seek a system availability of 90% or higher. If you have an availability percentage below this rate, you might consider reviewing your current maintenance programs, equipment and preventative maintenance schedules.

Related: How To Become a Maintenance Engineer

Example of calculating system availability

Here's an example you can review to help you calculate system availability:

Tennent Industries wants to measure its system availability for one of its production machines. They decide to analyze one month of data. They scheduled the machine to operate for seven hours daily. The total number of days scheduled for production was 22. They multiply seven by 22 to discover the uptime of the machine for the one-month period is 154 hours. The company's maintenance team tracked 12 hours of downtime for the machine because of preventative maintenance and unscheduled downtime.

To discover system availability, they added the 12 hours of downtime to the 154 hours of uptime. This results in 166. Then, they divide the uptime hours, or 154 hours, by that result of 166 hours. The final result is 0.9277. Multiplying this number by 100, they discover their system availability is 92.77% for the month. Tennent Industries analyzes this result and determines it's above their desired availability percentage. This signifies they have effective preventative maintenance and upkeep programs.