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

MTTF Formula

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


  • 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?

  1. First, determine the total number of units.

    For this example, there are 3 different pieces of equipment that run at a manufacturing plant.

  2. 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.

  3. 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