MTBF, MTTR and availability calculator
Calculate mean time between failures, mean time to repair and availability of a machine or system from its operating and repair history.
Track failures and availability
Tracking failures over time? The MTBF, MTTR and availability template is a ready-made starting point for logging failure and repair data.
How it is calculated
MTBF = operating time ÷ number of failures. MTTR = total repair time ÷ number of failures. Availability = MTBF ÷ (MTBF + MTTR).
Worked example
1000 h operating, 20 h repair, 4 failures: MTBF = 1000 ÷ 4 = 250 h, MTTR = 20 ÷ 4 = 5 h, availability = 250 ÷ 255 = 98.04 %.
Steps
- Enter the operating time for the period from the machine log.
- Enter the total corrective repair time and the number of failures for the same period.
- Read MTBF, MTTR and availability.
Frequently asked questions
Is this the same as OEE availability?
No. This is inherent availability from failures and repairs only. OEE availability also includes changeovers and other stops, so it is usually lower.
Should planned maintenance count as repair time?
No. Use corrective repair time for MTTR. Planned maintenance is normally left out of failure-based MTBF and MTTR.
What if there were no failures?
MTBF and MTTR are per failure, so they are undefined with zero failures. Use a longer period, or report that no failures were observed.
References
IEC 60050-192 (dependability vocabulary); MIL-HDBK-338B (inherent availability A = MTBF ÷ (MTBF + MTTR)).
Estimates for information only. Verify critical values with a qualified engineer or your supplier standards.