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PERT Calculator

Plan your personal and work-related projects efficiently with the help of this online PERT calculator.

Pessimistic:

Optimistic:

Most Probable:

PERT Estimate Unit:

Desired Completion:

Standard Deviation Unit:

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With this PERT calculator, you can quickly determine the expected completion time of a project, its standard deviation, and the probability of finishing within a target timeframe. This tool is designed to help contractors and project managers provide accurate project time estimates efficiently. For additional calculations, you can also check our expected value calculator.

Understanding PERT

PERT (Program Evaluation and Review Technique) is a project management method used to estimate the time required to complete tasks. It is a variation of the Critical Path Method (CPM) and helps schedule tasks while providing a realistic project completion timeline. PERT calculations use three types of time estimates:

Optimistic (O): Best-case scenario if everything goes smoothly.
Most Likely (M): Expected time considering normal conditions.
Pessimistic (P): Worst-case scenario accounting for risks and delays.

PERT Formulas

Expected Project Duration (T_E):

T_E = (O + 4M + P) / 6

Standard Deviation (SD):

SD = (P - O) / 6

Where:

T_E = Expected project duration
O = Optimistic time estimate
M = Most likely time estimate
P = Pessimistic time estimate
SD = Standard deviation of project duration (learn more)

If manual calculation seems complex, a PERT calculator can quickly perform these computations.

PERT Calculation Example

Suppose a contractor provides the following estimates for a project:

Optimistic (O) = 14 months
Most Likely (M) = 16 months
Pessimistic (P) = 22 months

Step 1: Calculate Expected Duration

T_E = (O + 4M + P) / 6

T_E = (14 + 4×16 + 22) / 6

T_E = (14 + 64 + 22) / 6 = 100 / 6

T_E = 16.67 months

Step 2: Calculate Standard Deviation

SD = (P - O) / 6

SD = (22 - 14) / 6 = 8 / 6

SD = 1.33 months

Thus, the expected project duration is approximately 16.67 months with a standard deviation of 1.33 months.

How the PERT Calculator Works

Using the PERT calculator is simple:

Inputs:

Optimistic Estimate (O)
Most Likely Estimate (M)
Pessimistic Estimate (P)
Desired completion time (optional)
Select units for PERT and SD
Click "Calculate"

Outputs:

Expected project duration (T_E)
Standard deviation (SD)
Probability of completion within the desired time (learn more)

FAQs

What Are The Six Steps In PERT?

Identify all project activities
Determine the sequence of activities
Create a network diagram
Identify the critical path
Estimate the time for each task
Update and revise the PERT chart as needed

What Are The Benefits of PERT Estimation?

Evaluates time and resources required
Provides clarity on all activities
Improves project action planning
Accounts for uncertainties and risks

Why is the 4 used in the PERT formula?

The “4” gives the most likely estimate (M) four times the weight of O and P, emphasizing the probable duration while considering best- and worst-case scenarios.

Why is PERT divided by 6?

Division by 6 averages the weighted sum: 1 (O) + 4 (M) + 1 (P), giving the expected project duration.

References:

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