Important Performance Testing Formulae

Performance Testing and Engineering are quantitative approaches in which numbers and formulae play a vital role. You can not think about Performance Testing without understanding the basic mathematics behind the testing technique. This article has some basic formulae that will help you to understand the logic and relationship between different performance testing terms. So, let’s start:

Little’s Law:

For Web Applications:

``U = IR * (IRT + TTT + P)``

where:

• U = No. of Users (User Load)
• IR = Iteration Rate (Iterations per second)
• IRT = Iteration Time i.e. Time to complete one iteration
• TTT = Total Think Time
• P = Pacing

For Web Services / API:

``U = T * (IRT + TTT)``

where:

• U = No. of Users (User Load)
• T = Throughput (Requests/calls per second)
• IRT = Iteration Time i.e. Time to complete one iteration
• TTT = Total Think Time

Concurrent User (per hour)

``CU = (NSavg * SDavg) / 3600``

where:

• CU = Concurrent Users
• NSavg = Average number of sessions per hour
• SDavg = Average Session Duration (in seconds)

Response Time

``RT = ND + SPT``

where:

• RT= Response Time
• ND = Network Delay
• SPT = Server Processing Time

Network Delay

``ND = NPD + QD + TD + PD``

where:

• ND = Network Delay
• NPD = Nodal Processing Delay
• QD = Queuing Delay
• TD = Transmission Delay
• PD = Propagation Delay

Service Time

``ST = BT / N``

where:

• ST = Service Time
• BT = Busy Time
• N = No. of transactions/requests processed during the busy time

Queue Length

``QL = X * QT``

where:

• QL = Queue Length
• X = Throughput; Request arrival rate
• QT = Time spent waiting in a queue for access to computing resources

Throughput (Rate)

``X = N / T``

where:

• X = Throughput (in seconds)
• N = No. of Request or Calls
• T = Total Time (in seconds)

Utilization

``Ut = BT / T``

where:

• Ut = Utilization
• BT = Busy Time
• T = Total Time (in seconds)

Average Utilization

``Uavg = (X * ST) / M``

where:

• Uavg = Average Utilization
• X = Throughput
• ST = Service Time
• M = Average Number of Servers

Important Calculators

If you are aware of more Performance Testing Formulae then write in the comment section.

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