How to calculate the 95th percentile

How to calculate the 95th percentile

The 95th percentile is a standard statistical measurement used to interpret performance data, particularly in traffic generation on an interface. It represents the value below which 95% of the data points fall, effectively ignoring the highest 5% of values to reduce the impact of short-lived spikes. This ensures that occasional high-usage moments don’t unfairly impact overall calculations, providing a more accurate and fairer representation of sustained usage compared to other statistical metrics like the average or median. 

Steps to calculate the 95th percentile

Follow the sequence of steps below to calculate the 95th percentile:
  1. Gather the dataset with numerical values recorded over a defined period.
    Suppose we have the following 20 data points (e.g., the CPU usage recorded at 20 different time intervals):
    90, 33, 83, 6, 93, 41, 49, 24, 53, 63, 81, 41, 33, 49, 87, 36, 46, 29, 119, 116
  2. Arrange all the values in ascending order.
    6, 24, 29, 33, 33, 36, 41, 41, 46, 49, 49, 53, 63, 81, 83, 87, 90, 93, 116, 119
  3. Calculate the index:
    1. P is the position in the sorted list.
    2. N is the total number of data points.
      P=N×0.95
      P=20×0.95=19
  4. If P is not a whole number, round it up to the nearest integer.
    Here, P=19 which is a whole number.
  5. Locate the value at the Pth position in the sorted dataset.
    The 19th value in the sorted dataset is 116.
So, the 95th percentile of CPU usage is 116%.
The unit of the 95th percentile depends on the measurement unit of the monitored parameter. For resource utilization metrics like CPU, memory, and disk usage, it is represented as a percentage (%). 

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