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How to Use the Top Down Estimation Tool in Primavera P6 Professional

Written on . By Tracy Mah

Article By: Tracy Mah

The Top Down Estimation Tool in Primavera P6 provides added functionality to perform high level top-down estimation for labor, non-labor units and material resources for the project. Basically if you have an idea of the total hours a resource will be working on a project, you can then allocate the proportion of hours that resource will be assigned to their work packages and tasks.

Estimation weights are manually assigned to the Work Breakdown Structure (WBS) elements and individual activities. The Top Down Estimation Tool will then distribute the resource units (hours) from the ‘top’ WBS elements ‘down’ to the activities.

The first step for top down estimation requires you to determine the total number of labor or nonlabor resource units to apply. There are two Estimation Methods available – by “Prior Experience” or by “Function Point”. Prior Experience means that you draw from previous project experience as a guide on how many hours you think that resource will need to complete all of their tasks. Function Point method is used for information technology projects which use special calculations and algorithms for their resource units of measure.

The second step for top down estimation is to determine Estimation Weights or the portion of hours the resource will be working for each work package or WBS. The next step is to figure out the Estimation Weights for the individual activities within each WBS.

For example, you predict the project will have 1000 hours of labor total.

  • The first phase of the project will require 20% of the resource’s hours. The second phase will require 30% and the last phase 50%.
  • You can assign Estimated Weights of 2, 3 and 5 respectively to each WBS phase.
  • The Estimated Weights do not have to be percentages as P6 will automatically convert the weights to a percent based on the sum of the all the weights.

For the first phase:

  • The Estimated Weight % is (2/10)*100% = 20%.
  • 20% of 1000 hours equals 200 hours to be spread over the phase one Activities.
  • The 200 hours will then be distributed according to the Estimated Weights of each Activity within that WBS node.

Let’s look at a simple project. In the WBS window, add a column “Est Weight”. I’ve assigned the weights of 2, 3 and 5 respectively to the three phases.

How to use Top Down Estimation.

Next in the Activities window, a General Laborer has been assigned to every Activity. We see that P6 automatically calculated a Total Budgeted Labor Units of 600 hours based on each Activity’s Original Durations and Budgeted Units/Time.

But we want to allocate 1000 hours total for our General Laborer where 20% of the 1000 hours is in Phase 1, 30% in Phase 2 and 50% in Phase 3.

I’ll add the “Est Weight” column and randomly assign some weights for the General Laborer resource to each Activity.

On the Menu Bar, select Tools then Top Down Estimation.

How to Use Top Down Estimation

In the Top Down Estimation tool dialog box, select “Estimate Labor” in “Resources Units to Estimate” field. For the “Activities to Estimate” field, select the top level of the Project’s WBS, unless you only want a specific WBS node to be estimated. In this example, the “General Laborer” is selected in the “Resource” field. Lastly, “Prior Experience” is selected under the “Estimation Method” and “1000h” is entered for the number of “Estimated Units”.

How to Use Top Down Estimation

Once all the information is entered, click the “Apply” button. Viewing the results shows that:

  • The thee WBS Phases have 200h, 300h and 500h allocated respectively.
  • Within each Phase, the Budgeted Labor Units are spread according to the ratio of the Estimated Weights entered.
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The Top Down Estimation tool is useful to help with high-level resource planning. It is also useful to quickly assign the budgeted hours for your resources if you know the proportion of how the hours should be spread over the work packages and activities.