This website provides information about reliability and maintainability analyses - specifically, MTBF and MTTF calculations.

MTBF is a basic measure of reliability for repairable items. It can be described as the number of hours that pass before a component, assembly, or system fails. It is a commonly-used variable in reliability and maintainability analyses.

MTBF can be calculated as the inverse of the failure rate for constant failure rate systems. For example: If a component has a failure rate of 2 failures per million hours, the MTBF would be the inverse of that failure rate.

MTBF = (1,000,000 hours) / (2 failures) = 500,000 hours

MTTF is a basic measure of reliability for non-repairable systems. It is the mean time expected until the first failure of a piece of equipment. MTTF is a statistical value and is meant to be the mean over a long period of time and large number of units. For constant failure rate systems, MTTF is the inverse of the failure rate. If failure rate is in failures/million hours, MTTF = 1,000,000 / Failure Rate for components with exponential distributions.

Technically MTBF should be used only in reference to repairable items, while MTTF should be used for non-repairable items. However, MTBF is commonly used for both repairable and non-repairable items.

Relex Software Corporation produces software that enables users to easily perform MTBF calculations and MTBF predictions, based on the failure rate of components in an assembly. Relex Software is a leader in R&M (Reliability and Maintainability) software analysis tools. We specialize in software, training courses, and seminars covering all aspects of reliability engineering. Our products are used by thousands of engineers worldwide in a variety of businesses.

Please visit the Links page for more online information about the Relex Software visual reliability software modules, and about MTBF and MTTF analyses in general.

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