System Availability Calculator

Work out system availability instantly with clear inputs, formula shown and shareable results.

About System Availability Calculator

Inherent availability of a component is MTBF/(MTBF+MTTR). Components in series multiply, so a chain of five components at 99.67% each gives only 98.35%. Operational availability further deducts planned maintenance, and multiplying its complement by 8760 gives expected annual downtime hours.

Formulas

Availability

A_component = MTBF / (MTBF + MTTR); A_series = A^n

Operational

A_operational = A_series x (8760 - planned downtime) / 8760

Worked example

With the default values below, System Availability Calculator returns Operational Availability of 97.0026%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Mean Time Between Failuresminimum 0.01 hours: 2,400 hours
Mean Time To Repairminimum 0.01 hours: 8 hours
Components In Seriesaccepts 1–50: 5
Planned Downtime Per Yearminimum 0 hours: 120 hours

Results

Operational Availability: 97.0026%
Single Component Availability: 99.6678%
Series System Availability: 98.3499%
Expected Annual Downtime: 262.6

Step by step

1Values used
2Availability
3Operational
4Operational Availability= 97.0026
5Single Component Availability= 99.6678
6Series System Availability= 98.3499
7Expected Annual Downtime= 262.6

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does adding components hurt so much?

Availabilities multiply. Ten components at 99% each give 90.4% system availability, which is why simplification is often more effective than improving individual items.

Which lever helps more, MTBF or MTTR?

Halving MTTR usually gives the same availability gain as doubling MTBF, and is far cheaper to achieve through spares, access design and trained crews.