Enter the total hours of operation and the total number of units produced to determine the mean time to failure (MTTF).

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## MTTF Formula

The following formula is used to calculate the mean time to failure.

MTTF = THO / TNU

- Where MTTF is the mean time to failure (hours/failure)
- THO is the total sum of all hours of operation of those units (hours)
- TNU is the total number of units

MTTF should not be confused with MTBF, which is the mean time between failures. This is explored in the calculator linked above.

## MTTF Definition

MTTF stands for mean time to failure. It describes the ratio of the total operational hours per production unit.

## Example Problem

How to calculate MTTF?

**First, determine the total number of units.**For this example, there are 3 different pieces of equipment that run at a manufacturing plant.

**Next, determine the total operational hours before failure.**The pieces of equipment ran for 4,000 – 5,000 – and 6,000 hours respectively. The total sum of these is 15,000 hours of operation.

**Finally, calculate the MTTF.**Using the formula above the mean time to failure is calculated to be:

MTTF = THO / TNU

MTTF = 15,000 / 3

MTTF = 5000 hours per unit