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About this tool
Compute mean time to repair, mean time between failures, failure rate and resulting availability from real incident data.
This calculator computes MTBF (mean time between failures = uptime ÷ number of failures), MTTR (mean time to repair = total repair time ÷ number of failures), the failure rate λ = 1 ÷ MTBF, and inherent availability A = MTBF ÷ (MTBF + MTTR). It is built for SREs, maintenance engineers and operations teams who track incidents over a window — a week, a month, a quarter — and want the standard reliability metrics from raw counts and hours.
Open MTTR and MTBF Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
MTBF, MTTR, failure rate and availability from three inputs, using the standard definitions.
Rejects impossible data such as repair time longer than the window or downtime with zero failures.
Shows the availability both as a percentage and as its equivalent number of nines.
Divide total operating (up) time by the number of failures in the observation window: MTBF = uptime ÷ failures. For example, a service up 714 of 720 hours with 3 failures has an MTBF of 238 hours. MTBF applies to repairable systems; for parts replaced rather than repaired, the analogous metric is MTTF.
MTTR measures how long a repair takes on average (total repair time ÷ failures), while MTBF measures how long the system runs between failures on average (uptime ÷ failures). Together they set availability: A = MTBF ÷ (MTBF + MTTR), so you can raise availability either by failing less often or by recovering faster.
Availability = MTBF ÷ (MTBF + MTTR), which is algebraically identical to uptime ÷ total time. With MTBF 238 h and MTTR 2 h, availability is 238 ÷ 240 = 99.17%, roughly two nines.
There is no universal number — it depends on the system and how MTTR is scoped (repair only, or detect-to-restore). Many software teams aim to restore user-facing service in under an hour, while hardware repairs are often measured in hours or days. The more useful practice is to define the clock consistently (when it starts and stops) and track the trend over time.
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