MTBF, MTTR and maintenance KPIs: formulas and examples
- MTBF = operating time ÷ number of breakdowns. It measures reliability.
- MTTR = total repair time ÷ number of repairs. It measures how quickly you recover.
- Availability = MTBF ÷ (MTBF + MTTR).
- They are only reliable if work orders record the start and end of each breakdown properly.
MTBF (mean time between failures) is calculated by dividing operating time by the number of breakdowns, and MTTR (mean time to repair) by dividing total repair time by the number of repairs. Together they let you calculate a piece of equipment’s availability. They are the basic indicators for knowing whether maintenance is working.
MTBF: mean time between failures
MTBF = total operating time ÷ number of failures
Example: a machine ran for 1,000 hours in a quarter and had 4 breakdowns. Its MTBF is 1,000 ÷ 4 = 250 hours. The higher, the more reliable. It is useful to compare similar equipment and to check whether an improvement (for example, a new preventive plan) reduces breakdowns.
MTTR: mean time to repair
MTTR = total repair time ÷ number of repairs
Example: the 4 breakdowns above added up to 12 hours of repair. The MTTR is 12 ÷ 4 = 3 hours. The lower, the faster the equipment recovers. A high MTTR may indicate a lack of spare parts, training or documentation.
Availability
Availability = MTBF ÷ (MTBF + MTTR)
With the data above: 250 ÷ (250 + 3) ≈ 98.8%. It improves if you reduce breakdowns (MTBF goes up) or repair them sooner (MTTR goes down).
Other KPIs worth measuring
| KPI | What it measures | Approximate calculation |
|---|---|---|
| Preventive compliance | Discipline of the plan | Preventive tasks done on time ÷ scheduled × 100 |
| Preventive/corrective ratio | Balance between anticipating and reacting | Preventive hours ÷ corrective hours |
| Backlog | Pending work | Open orders or their estimated hours |
| Response time | Speed from the request to the intervention | Average between the creation and the start of the work order |
| Cost per asset | Where the money goes | Labour + material + external costs of its work orders |
Common mistakes when measuring
- Incomplete data: if the start and end time of each breakdown is not recorded, the calculations are worthless.
- Mixing different equipment in the same average.
- Chasing a number instead of understanding the cause of the breakdowns.
Indicators calculated from your work orders
Mantenplan calculates MTBF, response times, costs and profitability of your interventions from the data technicians record.
Try MantenplanFrequently asked questions
What is a good MTBF?
There is no universal value: it depends on the type of equipment and its use. What is useful is to compare a piece of equipment’s MTBF with its own evolution and with similar equipment.
What is the difference between MTBF and MTTF?
MTBF is used for repairable equipment (time between failures). MTTF (mean time to failure) is used for items that are replaced rather than repaired.