MTTR stands for mean time to repair: the average time it takes to fix a failed asset and return it to service. It is calculated by dividing the total repair time in a period by the number of repairs. In facility management, MTTR is one of the main measures of how quickly corrective work orders are resolved.
The MTTR formula
The formula itself is simple: MTTR = total repair time ÷ number of repairs. Only completed corrective jobs count. Planned work is measured separately, through PPM attainment.
You will also see MTTR expanded as mean time to restore, recover or resolve, particularly in IT service management. The arithmetic is the same, but the start and stop points can differ, and that is the detail to watch whenever two MTTR figures are compared.
A worked example
Take six corrective work orders raised on the HVAC system of an office tower in one month. Their hands-on repair times, from the technician starting work to the unit cooling again, are listed below. They add up to 18 hours across 6 repairs, so MTTR is 18 ÷ 6 = 3.0 hours.
- FCU not cooling on level 12: 2.0 hours
- AHU drive belt failure: 1.5 hours
- Chilled water valve actuator fault: 3.0 hours
- Condensate pump failure, including 4.0 hours waiting for a replacement pump: 6.5 hours
- Room thermostat fault: 1.0 hour
- FCU fan motor replacement: 4.0 hours
Why the clock rules change the answer
What counts as repair time is the part that needs agreeing. Reliability engineers often measure only the hands-on repair, from the start of work until the asset is working again. FM contracts more often measure from the moment the job is logged until it is resolved, which includes response and travel. Both are legitimate; mixing them is not.
Apply that to the example. If the contract excludes time waiting for parts, the condensate pump job drops to 2.5 hours, the total becomes 14 hours and MTTR falls to about 2.3 hours. If the contract measures from logging instead, and the six jobs took a combined 6 hours to attend, MTTR rises to 24 ÷ 6 = 4.0 hours.
Same jobs, three different answers. The KPI schedule should therefore state the start and stop points, the permitted pauses for parts, access or client approval, and whether a temporary make-safe counts as a repair. Report MTTR by priority and trade rather than as one blended figure, and read it alongside first-time fix rate and repeat work orders, because closing a job at the temporary fix and raising a new order for the permanent repair flatters it. Our guide to work order KPIs sets out the formulas, gaming risks and data requirements for MTTR and eleven other measures.
MTTR, MTBF and availability
MTTR tells you how quickly things are fixed. Its partner, MTBF (mean time between failures), tells you how often they break: total operating time divided by the number of failures. Together they give availability, the share of time an asset is ready to work: availability = MTBF ÷ (MTBF + MTTR).
A chiller with an MTBF of 400 hours and an MTTR of 8 hours is available 400 ÷ 408 of the time, or about 98.0%. Halve MTTR to 4 hours and availability rises to about 99.0%, without the chiller failing any less often. For critical plant in a Gulf summer, where losing cooling can empty an office floor or a mall concourse within hours, that difference matters.
Common questions
How do you calculate MTTR?
Add up the repair time for all completed corrective jobs in the period and divide by the number of jobs. For example, 18 hours of repair time across 6 jobs gives an MTTR of 3 hours. Agree in advance when the clock starts and stops, and which delays are excluded.
What is the difference between MTTR and MTBF?
MTTR measures how long repairs take; MTBF (mean time between failures) measures how long an asset runs between failures. A lower MTTR and a higher MTBF are both better, and together they determine availability.
What is a good MTTR?
There is no universal figure, because MTTR depends on the asset, the trade, the priority and how the clock is defined. A lift entrapment, a leaking valve and a chiller compressor failure have very different realistic repair times. Set targets per priority and asset class from at least three months of your own data.
How can you reduce MTTR?
Improve helpdesk triage so the right trade attends with the right information, hold spares for critical assets based on failure history, and give technicians the asset history and manuals on mobile by scanning the asset tag. BMS alarms help catch faults before a tenant reports them, and root-cause work on repeat failures removes jobs altogether rather than only speeding them up.