Mean Time to Failure: How to Calculate and Use MTTF

MTTF Mean Time to FailureBrand new assets should give you lots of operation time before they break down. Right? To be sure, calculating MTTF or Mean Time to Failure will help you be prepared for the inevitable from the get-go.

MTTF can help reduce inventory lead time, increase quality control and better prepare you for the first time that new machine or device breaks down. We’ll tell you everything you need to know and even give you a few shortcuts along the way.   

Mean time metrics overview

MTTF is one leg in the proverbial three legged stool of maintenance mean time or incident metrics. 

When combined with the other mean time metrics, MTTF provides useful information for maintenance teams to help them predict and manage equipment failure. 

In this post, we will discuss how to calculate and use MTTF. But make sure you read our posts on MTBF and MTTR to get a complete understanding of their value, how and when to use them, and what they mean for your organization. 

What is MTTF, or mean time to failure?

Mean Time To Failure is the average time a non-repairable item or device is excepted to last in operation until it needs to be replaced. It is a very basic measure of reliability for systems that cannot be repaired. In the manufacturing industry, MTTF is used to determine the dependability of manufactured products. 

Mean time to failure (MTTF)

Understanding MTTF vs MTBF (mean time between failures) can be a challenge because they are somewhat similar. Here is the key distinction.


  • Measures the time to failure for non-repairable assets
  • Is the amount of time between the device’s first day of use and the last
  • Represents the entire lifecycle of a product or device 


  • Measures time between failures for repairable items
  • Takes failure rate or number of failures into account
  • Predicts when an item may need to be repaired next

Why MTTF metrics are important

Mean Time to Failure helps an organization estimate the lifespan of products and equipment that they know they will need to keep on hand for necessary replacements. Some common examples are: 

  • Fan belts in automobiles
  • Light bulbs in our homes and offices
  • Batteries used in vehicles or other large equipment

What MTTF means for your organization

MTTF is particularly useful as a reliability metric. Engineers can use it to estimate how long a component of critical machinery or equipment may last. Having an awareness of your MTTF allows you to: 

  • Evaluate the effectiveness and quality of equipment and components
  • Forecast equipment and component replacement needs and plan preventive maintenance tasks
  • Plan for proper inventory management to ensure the resources and replacement parts are available for repairs

Shorter MTTF means more frequent replacements. And more replacements mean more downtime, less uptime, higher costs, and other impacts on productivity. Learning how to extend it can be very worthwhile.

When to measure your mean time to repair

If you are planning to invest in a new process that requires specific equipment, it is important to know how long the equipment is expected to last. This will help you plan steps in the process, and determine your project budget. 

MTTF helps determine spending on both your capex and opex budgets. How often will you be replacing things, and at what costs? 

You can sometimes find information about MTTF from the OEM but they can sometimes be misleading. Reach out to other maintenance managers to get their input if you can. And always run your own MTTF reporting to keep track of your asset lifespans

How to calculate MTTF 

Calculating MTTF doesn’t have to be hard. As long as you’ve tracked the total hours of operation and the number of components you use in the same length of time, you have everything you need. 

If you use a CMMS like Limble, it likely automatically calculates this for you from the data you have. But MTTF can be calculated easily using tools like Microsoft Excel. We’ll show you how. 

The data needed to find your MTTF

Because MTTF is an average lifespan of a piece of equipment or component, you will be calculating it for something that you have or use many of. MTTF is calculated as the total time of operation, divided by the total number of units tracked.

A simple MTTF formula

How to calculate MTTF

Let’s assume we tested 3 desktop hard drives. The first one failed after 500,000 hours, the second one failed after 600,000 hours, and the third hard drive failed after 700,000 hours in use. MTTF in this instance would be:

MTTF = (500,000 + 600,000 + 700,000) / 3 units

MTTF = 1,800,000 / 3

MTTF = 600,000 hours

We can now assume that this particular type and model of hard drive is likely to fail after 600,000 hours of use and we can plan replacements accordingly.

How to calculate MTTF using excel and other reporting tools

While it is good to know how to measure MTTF by hand, it is impractical to plan to do it that way every time. A simple spreadsheet makes calculating MTTF easy as long as you are making note of the correct data. But a CMMS software basically does all the work for you.

With a CMMS like Limble, equipment failures are logged through the work request process, tracking downtime and operational time automatically. As a result, your mean time metrics begin calculating the second you begin using the system, building you a dashboard of useful key performance indicators (KPIs)

However, if you aren’t quite ready to take the CMMS plunge, we have created a handy calculator. Download it, and see how nice it is to have the work done for you!

Mean Time Metrics Calculator

Just getting started with maintenance metrics? Use this helpful calculator with formulas and calculations.

How to increase MTTF and improve productivity

Increasing your MTTF can greatly improve your productivity because you are ensuring that you get the longest lifecycle possible out of your assets, and that you are ready and prepared with a replacement when it fails. Below are a few steps you can take to increase your MTTF: 

  • Use the best quality items you can find and that your budget allows. Parts that are made from more durable materials and have gone through a thorough quality control process may cost more but will last longer, requiring fewer replacements in the long run. Limble lets you keep track of your preferred parts and vendors, as well as the long-term cost to measure your ROI. 
  • Take action to improve the lifespan of the asset. Make sure the devices are used for their intended purpose and in the conditions (humidity, heat, pressure, voltage, etc.) they are designed for. You can store equipment operating and maintenance manuals in Limble to ensure it is properly installed/retrofitted every time. 
  • Use your time, budget, and resources wisely. Because you are not planning to fix anything, scheduling maintenance is not an option here. You can wipe off the dust or run high-level diagnostics to estimate remaining useful life, but it is important to use your resources where they count.


By now you should have a full understanding of MTTF, its value, and how to increase it to improve your productivity. 

Tracking your MTTF and other failure metrics will give you the knowledge and power you need to maintain a healthy maintenance budget and avoid large, unexpected equipment replacement costs. 

That being said, good incident management can be a lot of work. Limble helps both on the global level for all assets as well as reporting on each individual asset. As long as you update each task with all the data, these maintenance metrics will be tracked automatically.

See for yourself what Limble can do for you, schedule a quick product demo or start a free trial.

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