Enter the total uptime (hours) and total downtime (hours) into the calculator to determine the % availability of a system.

## % Availability Formula

The following formula is used to calculate the percentage availability of a system.

%A = UT / ( UT + DT ) *100

- Where %A is the percentage availability
- UT is the total uptime (hours)
- DT is the total downtime (hours)

## 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? **Availability should include both planned and unplanned downtime. While a planned downtime can be expected and understood by customers, it is still a portion of time in which the customer does not have access to a system. The system is still unavailable.

**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.