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What are MTBF, MTTF, and MTTR (with simple examples)?

Published 2023-10-24 by Alvaro Oberon (a 2.1 minute read) | Back to the main page

Introduction

MTBF, MTTF, and MTTR are basic maintenance efficiency and effectiveness indicators for measuring equipment maintenance management performance. Let's look at each one in detail.

MTBF - Mean Time Between Failures

MTBF is an acronym of "Mean Time Between Failures", and quantifies the average time between repairable failures of a system. The higher the time between failures, the more reliable the system. The goal for most companies is to keep MTBF as high as possible, putting hundreds of thousands of hours between issues.

MTTF - Mean Time To Failure

This is the average time until a non-repairable failure. It is used to measure the lifespan of a product that cannot be fixed or maintained, such as a light bulb or a battery. The higher the time to failure, the longer the product lasts.

MTTR - Mean time to repair

MTTR is the average time it takes to repair a failed system. It is used to measure the efficiency and effectiveness of maintenance processes and resources. The lower the time to repair, the faster the system can be restored to normal operation.

Practical examples

MTBF

  1. What functional location or equipment will you be analyzing (this one ids obvious!)
  2. What time period are you looking at? (e.g. one year)
  3. (A) How many times did the equipment fail during the above period? (e.g. 4 times)
  4. (B) How many hours did the equipment run for? (e.g. 8 hours per day * 6 days per week * 53 weeks = 2,496 hours)

MTBF is simply calculated by (B) / (A) => 2,496 / 4 = 624 hours.

MTTF

  1. (A) A light bulb failed 3 years after installation
  2. (B) Another of the same time failed 2.5 years after installation
  3. (C) Yet another failed 2.6 years after installation
  4. (D) Get the number of failures of the same type (in this example, that's 3 failures)

The MTTF is ((A) + (B) + (C)) / (D) => (3 + 2.5 + 2.6) / 3 = 2.7 years.

MTTR

  1. (A) On one occasion, the equipment failed and it took 5 hours to repair.
  2. (B) on another occasion, the equipment failed yet again but this time it took 3 hours to recover.
  3. (C) the number of failures we are considering (in this case it failed 2 times, so that will be 2).

The MTTR will therefore be ((A) + (B) )/ (C) => (5 + 3) / 2 = 4 hours.

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