MTBF (Mean Time Between Failures) is the average time a repairable system operates between consecutive failures. It equals total uptime divided by the number of failures. Higher MTBF means more reliable equipment.

What is the difference between MTBF and MTTF?

MTTF (Mean Time To Failure) applies to non-repairable items — it measures how long a component lasts before its first and only failure. MTBF applies to repairable systems and is MTTF + MTTR. For most software services, MTBF is the relevant metric.

MTTR (Mean Time To Repair or Mean Time To Recover) is the average time required to restore a system after a failure. It equals total downtime divided by the number of failures. Lower MTTR means faster incident resolution.

How is availability calculated?

Availability = MTBF / (MTBF + MTTR) × 100%. It represents the percentage of time a system is operational. 99.9% availability ("three nines") allows about 8.76 hours of downtime per year.

What time units should I use?

Use any unit consistently — hours are most common in SRE. The calculator works in whatever unit you choose; just make sure observation period, downtime, and the resulting MTBF/MTTR are all in the same unit.

What does "number of failures" mean?

It is the count of distinct incidents or failure events in the observation period, not the number of affected users or requests. Each incident counts as one failure regardless of severity.

MTBF Calculator

Name: MTBF Calculator
Availability: InStock
Author: Nham Vu

Calculate MTBF, MTTR, MTTF, and availability percentage from your failure and downtime data.

Reliability Inputs

Time Unit

Observation Period (hours)

Total time window being analyzed (e.g. 8760 = 1 year in hours).

Number of Failures

Total count of distinct failure incidents in the period.

Total Downtime (hours)

Sum of all downtime across every failure event.

Quick Examples

Fill in the inputs and click Calculate
to see your reliability metrics.

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Summary

Calculate MTBF, MTTR, MTTF, and availability percentage from your failure and downtime data.

How it works

Enter the total observation period (hours, days, or minutes).
Enter the total number of failures recorded in that period.
Enter the total downtime accumulated across all failures.
The calculator derives uptime, then computes MTBF, MTTR, MTTF, and availability.
Results update live as you type — copy any value with one click.

Use cases

SRE teams tracking service reliability against SLA targets.
DevOps engineers benchmarking infrastructure stability.
Hardware engineers estimating component lifespan.
Incident post-mortems requiring availability percentage evidence.
Capacity planners modeling maintenance windows.
Quality assurance engineers computing product reliability scores.
System architects comparing redundancy configurations.
Procurement teams evaluating vendor uptime guarantees.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu