What is MTBF and MTTF? How to calculate?

MTBF and MTTF are two important reliability metrics used to assess the reliability of various systems and products. MTBF stands for Mean Time Between Failures, while MTTF stands for Mean Time To Failure. In this article, we will explore the definitions, differences, and calculation methods for these two metrics.

What is MTBF?

MTBF is the measure of the average time between the failures of a system or component. It is calculated by dividing the total operating time of the system by the number of failures that have occurred during that time. MTBF is typically used to assess the reliability of products that can be repaired or replaced, such as electronics and appliances.

What is MTTF?

MTTF is the measure of the average time it takes for a system or component to fail. It is calculated by dividing the total operating time of the system by the number of failures that have occurred during that time plus the time required to repair or replace the failed component. MTTF is often used to assess the reliability of products that cannot be repaired or replaced, such as light bulbs or batteries.

Differences between MTBF and MTTF

The primary difference between MTBF and MTTF is the inclusion of repair or replacement time in MTTF calculations. MTBF assumes that all failed components have been immediately replaced or repaired, while MTTF takes into account the time required to replace or repair the failed component. MTTF is typically a shorter measurement than MTBF because it includes the time required for repair or replacement.

Calculation methods

MTBF and MTTF can be calculated using similar methods. Both metrics require the total operating time of the system or component and the number of failures during that time. The formula for calculating MTBF is:

MTBF Calculation

MTTF Calculation

It’s also worth noting that both MTBF and MTTF can be used to calculate many other important reliability metrics, such as availability, maintainability, and uptime.

MTBF and MTTF are two essential metrics used to assess the reliability of systems and components. While they are similar in calculation methods, they have different applications and results. MTBF is used primarily for products that can be replaced or repaired, while MTTF is used for products that cannot be replaced or repaired. By understanding these metrics and how to calculate them, engineers and manufacturers can make informed decisions to improve product reliability and performance.
Overall, accurate calculation of fatigue life is critical to designing reliable and durable electronic equipment. By carefully considering the types of cyclic loading, materials selection, and environmental conditions that may impact the component, and using appropriate tools and methods, engineers can design electronic components that are more likely to perform to expected standards over their expected lifespan.

Examples 1

Suppose a company wants to determine the MTTF of a power supply unit (PSU) that is expected to last for about 5 years. They know that the PSU will be operating continuously, and they have estimated that the failure rate of the PSU is approximately 0.1% per year. To determine the MTTF, they would first calculate the average time between failures (TBF).

TBF = 1 / Failure Rate
TBF = 1 / 0.001
TBF = 1000 hours

Then they can calculate the MTTF by multiplying the TBF by the total lifespan of the PSU:

MTTF = TBF × Expected lifespan

MTTF = 1000 hours × 43800 hours (5 years)

MTTF = 43,800,000 hours

Therefore, the MTTF of this power supply unit is approximately 43.8 million hours.

Examples 2

Suppose an organization needs to calculate the MTBF of a data storage system. The system has been in operation for 6 months and has experienced 1 failure during that time. To calculate the MTBF, they would use the following formula:

MTBF = Total operating time / Number of failures

MTBF = 4380 hours (6 months) / 1

MTBF = 4380 hours

Therefore, the MTBF of the data storage system is 4,380 hours.

Examples 3

Suppose a company wants to calculate the MTTF of a digital camera expected to last for about 3 years. They have estimated that the failure rate of the camera is approximately 0.03% per year. To calculate the MTTF, they would use the formula described in Example 1.

TBF = 1 / Failure rate

TBF = 1 / 0.0003

TBF = 3333.33 hours

MTTF = TBF × Expected lifespan

MTTF = 3333.33 hours × 26280 hours (3 years)

MTTF = 87,598,320 hours

Therefore, the MTTF of this digital camera is approximately 87.6 million hours.

Keep in mind that these examples are simplified and for educational purposes. Accurately calculating MTTF and MTBF can be quite complex and requires detailed knowledge of the specific equipment being analyzed.

In this article, we have explained in detail “What is MTBF and MTTF? How to calculate?” which is a frequently asked question in the aviation industry. If you are interested in aviation and engineering fields, you can read NASA as a global source and other articles on the TAELCO Blog as a Turkish source.