# How to Calculate the MTBF

Save

Reliability engineering began in the aviation industry, where unreliable equipment often meant the difference between life and death. MTBF, or mean time between failure, is a statistical model that has become a common tool used to quantify reliability in the assessment of mechanical products. Increasingly, MTBF is employed in mechanical and system design, product procurement, plant operations and product and plant maintenance.

## MTBF Basics

• The MTBF is a mathematical model that describes the mean or average time that a machine operates before repairable failure occurs. Inherent in the definition of MTBF is the idea that repair will occur. MTBF is perhaps the simplest and most accurate method of determining the reliability of an engine or other type of machinery. Reliability is the likelihood that a device will function optimally for a specific length of time. The integrity and quality of a product are an integral part of MTBF.

## Calculating MTBF

• To determine the MTBF, a trial period where machinery runs to its designed purpose and then fails is required for accurate assessment. MTBF = t/r where t = total run time and r = number of failures during that time. Total run time (t) is the sum of operational times. For example, if a system runs for 50 hours before failure, then 48 hours and then 51 hours, the total run time would be 50 + 48 + 51 = 149. Failures (r) would be 3 in this example, which would give an MTBF of 149/3 or approximately 49.7 hours of operation before failure occurred. It is important to note that when collecting data, mean operation time includes only the time when machinery is functioning. It does not include time for maintenance, repair or or otherwise nonoperational hours.

## Influencing Factors

• MTBF is considered an important marker of reliability, but it does have limitations. MTBF predictions are commonly practiced during the normal life period of a device. Normal life period is defined as the time when the lowest rate of failure occurs. As machinery ages, failure rate naturally increases. Because of this, most MTBF data is not averaged in. Additionally, reliability tests are performed under advantageous circumstances where dust, humidity, temperature, movement and other factors are controlled. Though reliability engineers consider the normal user and everyday factors of use, discrepancies such as shortened MTBF sometimes occur in real-world scenarios.

## Formula in Action

• Whether you are interested in purchasing a new computer, a new car or an entire factory full of equipment, the MTBF of a product is a tool that can inform the decision-making process. For those who work with mechanics, knowledge of MTBF provides insight into challenging repairs. Knowing the MTBF of parts and components allows maintenance schedules to be created before problems occur.

## References

• Photo Credit David De Lossy/Photodisc/Getty Images
Promoted By Zergnet

## Resources

### You May Also Like

• How to Calculate MTBUR from MTBF

Equipment maintenance and repairs can be a significant portion of your company's expenses. Analyzing performance data such as the mean time between...

• How to Convert FIT to MTBF

Space scientists have the task of managing long-life projects that last years, and eliminating failure of mission-critical equipment. Engineers predict the in-service...

• How to Calculate a MTTF

Most of the equipment your business relies on will need to be replaced at some point. Calculating how likely failures are and...

• How to Calculate Inter-rater Reliability

The term inter-rater reliability describes the amount of agreement between multiple raters or judges. Using an inter-rater reliability formula provides a consistent...

• How to Determine Copier Life

A copier's acquisition and operating costs make it a sizable investment for home offices or small businesses. In exchange for that chunk...

• How to Service Your Garden Tractor Hydrostatic Transmission

A hydrostatic transmission uses pressure plates to allow energy to flow from the engine to the transmission. The transmission does not use...

• How to Calculate a Duty Cycle

Many electrical devices do not operate continuously but instead have a discrete amount of time during which they are active and then...

• How to Calculate Failure Rates

Calculating failure rates is important in everything from manufacturing car parts to shooting baskets in a game of basketball. A failure rate...

• What Is Win Rate?

Win rate, or winning percentage, is one of the most telling statistics when it comes to team or individual success in sports....

• How to Calculate MTBF From Failure Rate

A common metric used when determining the reliability of a specific model of computer hardware is MTBF. MTBF, Mean Time Between Failure,...

• How to Calculate Reliability & Probability

Probability is a measure of how likely something is to happen (or not happen). Measuring probability is usually based on a ratio...

• How to Calculate Cpk Value

Cpk, or the process capability index, measures how closely a process is performing relative to specification limits. Cpk can be used to...

• How to Calculate Availability of Machinery

Companies whose sole mission is product production on a massive scale are heavily reliant upon the machinery that is used in this...

• How Long Should a CPU Fan Last?

The CPU (Central Processing Unit) fan in a computer keeps the processor from overheating and suffering damage. When the fan fails, the...

• Examples of Key Performance Objectives

Corporate analysts work with a wide array of performance objectives, and many analysts produce periodic reports to show the status of certain...

## Related Searches

Check It Out

### Can You Take Advantage Of Student Loan Forgiveness?

M
Is DIY in your DNA? Become part of our maker community.