Maintainability Definition & Calculations

Answered June 04 2019

What is maintainability?

Maintainability refers to the ease with which maintenance activities can be performed on an asset or equipment. Its purpose is to measure the probability that a piece of equipment in a failed state can be restored to normal operating conditions after undergoing maintenance.

How to measure maintainability

To measure the maintainability of an asset, you need to be able to quantify the amount of effort that is put into performing maintenance on that asset. While there are many methods to calculate the effort exerted, the most common way is simply by calculating the average time it takes to repair a piece of equipment. This might sound familiar because you are measuring the mean time to repair (MTR) , which is also typically used as a performance indicator metric.

The MTR, also known as MTTR, quantifies the average time that it takes to restore an asset to its normal operating conditions after experiencing a failure or breakdown. In formula form:

MTR = Total downtime (hours) / Number of failure events

Total downtime is the total time it takes to repair the asset and bring it back online, and the number of failure events is the total number of breakdowns that an asset experienced.

A lower MTR would correspond to a higher level of maintainability and, conversely, maintainable assets take less time to repair.


Maintainability vs. reliability

Maintainability picks up where reliability might fall short. While reliability characterizes how long an asset can operate without issues, maintainability describes the likelihood that the same asset can be restored once a failure does occur .

Think of maintainability as something that you want to have in the event of an unforeseen failure. While you should strive for reliability to be as high as possible, high maintainability levels can act as a back-up plan for instances where a breakdown does occur. Together, these qualities create higher performance levels for a facility because you are able to perform work continuously.

4 Factors that affect maintainability

1. Better training for your team

Training your team is crucial to the maintainability of your assets. Their understanding and attitude towards machine repairs will determine the quality of work performed!

2. Maintenance drawings and checklists

Better documentation of asset knowledge and procedures will boost the maintainability of your assets since repairs will be more standardized and repeatable.

3. Standardizing equipment and inventory

By standardizing the equipment and inventory in your facility, you improve interchangeability. The implications of interchangeability are faster repairs and reducing the amount of time your assets spend offline after a failure.

4. Increasing planned (vs. unplanned) maintenance

Increasing planned and preventive maintenance will reduce the amount of unscheduled downtime of your assets.

Improving maintainability

Improving the process of actually doing repairs increases the maintainability of an asset and of the plant. While benchmark MTR values vary across different types of equipment used in different industries, working to keep MTRs low is a basic step to improving maintainability.

Properly documented repair procedures and availability of repair tools and materials can significantly reduce the time it takes to restore broken down equipment. A  computerized maintenance management system (CMMS) can help to not only keep accurate MTR records but also more efficiently document repair history data. Such historical records can increase the maintenance team’s ability to repair assets more efficiently.


Overall, the maintainability of your equipment and systems depends on providing better training to your team, more documentation of procedures, and increasing planned maintenance. In conjunction, these factors will improve availability and reliability, and simultaneously decrease downtime for your equipment.

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