using the pmbok estimate activity resources processEstimate activity resources.

There is a fundamental formula that ties together the duration of an activity against the amount of work effort required, and the resources needed to complete that work within the estimate activity resources process:

Activity duration = work effort/human units. For typical activities the duration will be measured in days, the work effort in hours and the amount of people required as a decimal fraction.

This particular process focuses on each activity within the schedule to calculate the resource requirements. Another factor that will need to be considered along with the hours work effort required, is the availability of the resources.

All of the above will combine end result in the project schedule which is developed in a later process within the time management group.

Here is how estimate activity resources fits in:

 estimate activity resources


Although the estimate activity resources forms part of developing the project time schedule, this process is normally undertaken in parallel with the process ‘estimate costs’ (which is a process within the cost management process group).

There are five inputs used to estimate activity resources:

Activity list. This is the prime input to estimate activity resources because each activity in the list will be studied so that appropriate resources can be estimated.

Activity attributes. These attributes will often include activity information such as the knowledge, skills, and experience for suitable individuals to carry out the activity. It may also include information on non human resources such as facilities, and materials and tools.

Resource calendars. This will cover both human and non human resources as the availability of an individual and then normal working hours will be just as important as the availability of resources such as a facility or heavy plant machinery as an example. This availability will need to be factored in to each activity and may have a bearing on the duration of each.

Enterprise environmental factors. Examples of why this may affect the resources required for an activity, could be the laws and regulations resulting in more or less work effort to carry out each activity, the environment within which the activity is to take place, or even the logistics concerning the use of resources.

Organisational process assets. Typical assets might be data from previous similar projects regarding the work effort for typical activities, or procedures that are mandated to carry out particular activities.

There are three outputs from the estimate activity resources process:

Activity resource requirements. This is normally a document that describes the number of resources for each schedule activity, and the knowledge, skills and experience of each. The work effort may be described as total hours, or as skills set per time period. An example for the latter might be three bricklayers for a period of two weeks. It is helpful to include assumptions and other detail in support of such estimates for each activity.

Resource breakdown structure. This is known as the RBS and is a similar graphical diagram to the WBS, however the diagram and each node describes the resources by category and type. A particular project may split the categories by knowledge or skills, or by department or group.

Project document updates. It is highly likely that the activity lists and activity attributes would normally get updated as a consequence of estimating activity resources. The resource calendars may be modified as well to pre-assign such resources.

There are five tools that may be used in the estimate activity resources process:

Bottom up estimating. It may prove difficult to estimate complex activities, and so it makes sense to break the down into smaller chunks of work so that these may be estimated and summed up from the this bottom level to the activity level itself.

Alternatives analysis. When considering the resource requirements for each activity (estimate activity resources), it may be helpful to consider alternative ways of carrying out the work as well as the resources needed to do so. This may result in a more effective and efficient way to carry out the activity such as buying procurement rather than designing in-house.

Expert judgement. As with all things in life, nothing beats experience. Those who are considered experts, or even those who have carried out similar tasks, should be involved in all aspects of estimating as this will result in a more realistic and achievable set of activities within the estimate activity resources process and the resulting schedule.

Published estimating data. This is often available in two forms; internal published sources based on historical data and experience of carrying out similar activities, and industry –standard tables of resources and effort. Within the building industry for example, there are standards tables describing the amount of person effort to construct standard frames when erecting buildings. Another example is the number of bricklayers needed to create a wall of standard dimensions.

Project management software. Applications such as Microsoft project can assist in storing and structuring information, and will allow swift calculations of alternatives or schedule possibilities. Such software is only a tool however, and the phrase ‘garbage in – garbage out’ applies here!

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David spent 25 years as a senior project manager for US multinationals and now develops a wide range of project-related downloadable video training products under the Primer brand. In addition, David runs training seminars across the world, and is a prolific writer on the many topics of project management. He currently lives in Spain with his wife Jude.

I hope you found my estimate activity resources article helpful!