Once you have MTBF and MTTR you can calculate availability, the share of time the machine is able to run. The formula is availability = MTBF ÷ (MTBF + MTTR). The denominator is one full cycle of running and repairing, and the numerator is the running part. Multiply by 100 to show it as a percentage.
Availability is useful because it turns two separate numbers into one that a line manager can act on. An availability of 99.2 percent on a machine that runs 500 hours a month means about 4 hours lost. You can improve that figure by raising MTBF (fewer failures) or lowering MTTR (faster repairs), and the formula shows which lever moves it more.
Failure rate is the flip side of MTBF. It is the number of failures expected per hour of operation, calculated as failure rate = 1 ÷ MTBF. People often find it easier to read when scaled up, for example failures per 1,000 operating hours. A failure rate that is rising is the same message as an MTBF that is falling.
Standard Procedure
- 1Take the MTBF and MTTR for the same machine and the same period.
- 2Add them together to get the full fail-and-repair cycle.
- 3Divide MTBF by that total and convert to a percentage.
- 4Calculate 1 ÷ MTBF and scale it to failures per 1,000 hours for easy reading.
Lesson Summary
- ✓Availability combines how often a machine fails with how long it stays down.
- ✓Failure rate is the reciprocal of MTBF and rises when MTBF falls.