How do I use this calculator?
Choose a calculation method, enter durations in compatible units, then select Calculate.
Calculator Operations:
- Use downtime with a preset or custom service period, or enter uptime and downtime directly.
- Choose allowed downtime to convert a target availability into downtime equivalents.
- Choose MTBF and MTTR for a steady-state inherent-availability estimate.
Use the actual measured service window for calendar months and business hours. Preset months, quarters and years use the stated average durations.
Use the calculate button when all known values have been entered and use the reset button when you want to clear the values from the calculator.
Calculate availability from service durations, allowed downtime from a target percentage, or inherent availability from MTBF and MTTR.
Related Calculators
- Service Level Calculator
- System Reliability Calculator
- Failure Rate Calculator
- MTBF to FIT Calculator
- Effective Capacity Calculator
- All Statistics Calculators
% Availability Formula
The following formula is used to calculate the percentage availability of a system.
- Where A is the percentage availability (%)
- UT is the total uptime (hours)
- DT is the total downtime (hours)
To calculate an availability percentage, divide the total uptime by the sum of the uptime and downtime, then multiply by 100.
Availability Definition
What is a percentage availability? A % availability is a ratio of the total time a system is running, known as uptime, and the total possible time a system could be running. The total time the system could potentially run is known as the sum of the uptime and downtime.
Example Problem
How to calculate % availability?
- First, determine the total uptime.
For this problem, we are looking at the total uptime and downtime of a web server over a month period. The total uptime is found to be 690 hours over the month.
- Next, determine the total downtime.
The total downtime of the server was measured to be 30 hours last month.
- Finally, calculate the percent availability.
Using the formula, the percent availability is found to be 690 / (690+30) *100 = 95.83%.
About Availability
Can availability be negative? An availability can never be negative. This would require either the total uptime or downtime to be negative, which is not possible.
Does availability include planned downtime? A raw customer-experience measure can include planned and unplanned outages. An SLA may exclude scheduled maintenance or define a different service window. Use the contract’s measurement rules consistently; this calculator alone does not establish SLA compliance.
Where is availability used? Availability is a term that can be used in many fields, but for the purpose of this page, the term is used to describe the total percentage of possible time that a service is available to a customer or user.
