One of our students sent a question in an e-mail wondering about weight calculations in his time schedule. He is in a situation where he has a time schedule that has master activities, those activities are cost-loaded as per the BOQ.
Later on, he found that some of those activities could be divided into smaller activities (First fix – Second fix – Third fix). This will make the time schedule more accurate and easier to monitor and control and spot the cause of the delay.
The problem is, on what criteria should I divide the master activity cost, over the sub-activities (First fix – Second fix – Third fix)? Should I divide the cost equally? Should I divide the cost according to each sub-activity’s duration?
So, we decided to create this guide, based on our best practice, to help you assign proper weight to your activities. Also in this guide, you will learn how to calculate the proper weight of every WBS in your time schedule.
So, this article will be divided into two main sections.
• How to calculate the cost of sub-activities (First fix – Second fix – Third fix)
• How to calculate the weight of each WBS in your time schedule
What is activities’ weight in time schedules?
Assigning weight to activities in your time schedule is a way to track, monitor, and control your time schedule. Every activity will have a weight according to certain criteria, like its duration, its level of complexity, its strategic importance, its cost, or the number of hours needed to finish that activity.
Why do we use weight in time schedules?
In most scenarios, our time schedules are cost-loaded, according to the BOQ. We use this cost later to calculate planned values and earned values to monitor our time schedule progress periodically.
In some cases, we might use the manhours of the activity as a reference to calculate the planned % and the actual %. In some other cases our BOQ is front-loaded, so the activities at the beginning of the project will have a cost higher than its usual cost. Some cost estimators do this to maintain a better cash flow. In that case, the planned % and actual % based on cost will not represent the actual progress on the site.
That’s why we use weight because weight could be independent of the cost and the BOQ. It also can be estimated and calculated upon the criteria that the project manager and the stakeholders agree on.
So at the start of the project, we agree on -for example- that construction activities will be 60% of the total weight, and the rest 40% will be 20% for the procurement and 20% for the engineering activities.
That’s how the weight works, in this article we will discuss different methods to estimate that weight. At the end of this article, you’ll find a video and another article to tell you the exact steps to add weight to your activities using Primavera P6 and Microsoft Excel.
How to calculate the cost of sub-activities (First fix – Second fix – Third fix)
The first thing that you have to keep in mind is that activities are different, we can’t divide all activities into fixes in fixed ways.
Some HVAC activities are divided into 2 or 3 fixes, other finishing activities like paint are usually divided into 3 or 4 fixes. Also, not all fixes are equal in cost or level of effort needed to finish them.
So, let’s agree that as there is no fixed way to divide activities, there is also no fixed way or a certain formula to divide the cost of the activities on its sub-activities.
The best solution for this problem is to discuss those certain activities with your site engineers team to agree on some weight or distribution of the cost, also you may discuss the matter with your project manager. By taking those actions, you guarantee that all involved parties are on the same page.
Our best practice and recommendations for this situation -if you can’t reach the site team or the project manager- is to divide the cost by the percentage of the manhours allocated for each sub-activity.
Activity A is divided into some activities (Activity A-1 – Activity A-2 – Activity A-3)
Our problem here is that we know the cost of activity A but don’t know how to divide the cost over the 3 sub-activities.
– Start with calculating how many manhours are needed for each activity.
Activity A = 200 manhr
– So, we will distribute the cost over the sub-activities as follows:
Activity A = 5000$ (From the BOQ)
A-1 cost = (60/200)* Activity A-Cost = 1500$
A-2 cost = (100/200)* Activity A-Cost = 2500$
A-3 cost = (40/200)* Activity A-Cost = 1000$
This is the easiest way to reach your goal and properly divide the cost. Now you can calculate the planned and earned values and percentages easily and monitor your project to know where exactly the variance or delays are coming from. This allows you to take effective and corrective actions at the right time.
How to calculate the weight of each WBS in your time schedule?
Now that we know how to estimate the weight/cost of each sub-activity properly, maybe you’re wondering, what about the WBSs of the time schedule.
On what criteria shall we estimate the weight of every trade in our time schedules?
Let’s start with the most common methods of estimating weight for the Work Breakdown Structures (WBS).
1- Based on Duration
I’m sure that the first this that came to your mind is creating the weight of the activities based on the duration of the activity. This is one of the methods, but I think it’s less effective than other better methods.
This method is based on distributing the weight over the time schedule activities and WBSs according to their durations only. That means that the activity that has more duration will have more weight, and that’s not accurate most of the time. For example, most of the HVAC devices are so high in cost but have a short time in your schedules as they are only brought to the site and connected with other parts and it’s done.
While other activities like painting will have more duration (and more weight) although they are much less in cost than other activities.
So, we only recommend using this method if you don’t have the activities’ costs (the BOQ) and don’t have the proper productivity rates and quantities to calculate the hours needed for each activity.
To learn how to create weight for your time schedule based on durations, I recommend you to watch this video:
2- Based on Cost
If you choose to build your weightage system on the activities cost, so your time schedule has to be fully cost-loaded. That cost loading should represent the actual values of the activities, this is important to avoid fake progress values resulting from front-loaded Bill of Quantities as we discussed at the beginning of this article.
In this case, we simply assume that we have 100,000 units of weight. We distribute those units over different WBSs and different activities according to the cost of each activity.
If a WBS has 20% of the cost of the total project, then it’ll have 20% of the weight units, and so on for the activities.
3- Based on Complexity
Sometimes we have complex activities that have lower costs and take a lot of hours, while other activities take less time but have huge costs. That’s when we prefer to base our weight according to the complexity of the activity.
You can create a matrix where you and your team divide the activities into certain groups up to their complexity levels. Then the higher the complexity, the higher the weight.
Using this method will let you show the team and the stakeholders how much of the complex work has been done. It lets you estimate the complexity level of the remaining work on your project too.
4- Based on Experience (Lessons Learned from Previous Projects)
When you work on many projects, you will build a sense of weight estimation for new projects. You will be able to have a look at the future and see the obstacles and the problems you may face in certain activities or certain work packages. According to your and your team’s experience, you can agree on a certain weight that looks like another weight from your previous projects.
For example, if you’re creating a schedule for a stadium in a certain country, and you had an experience before in the same country there will be some problems in mobilization. You can also estimate that the procurement activities in this project are the most important part as once they’re delivered to the project, you consider the hard part of the project to be done.
Based on that experience, you can increase the weight of the procurement WBS and decrease the construction weight %.
Another example is if you’re planning for a unique structure, that’ll have so many challenges in creating the engineering designs and the shop drawings. In that case, you should increase the Engineering WBS weight %.
Always remember to record the fundamentals on which you build your weightage system on, and confirm with your project manager, consultant, and client. The most important thing in progress calculation is agreeing on the same basics and being on the same page.
This is important for you to avoid any conflicts in the future between any stakeholders on the way that you calculate the progress.
5- Based on the resources needed
As you plan for your project, you load your time schedule and activities with resources. This resource allocation is when you know how many hours each activity will need to be finished. According to that, you calculate how many workers you need on each day of your project.
In our opinion, this is the best way to build your weightage system. Resource hours for each activity are a great representation of the level of complexity of the activity. So, if your schedule is resource-loaded (has resources on each activity), you can build your weightage system on those resources budgeted units.
Exactly like we did at the beginning of the article when we distributed the manhours of Activity A over its sub-activities, we can distribute the weight of the project over the WBSs and the activities of the whole project.
Total Project Hours = 550,700 manhours
Engineering = 100,700 manhours
Procurement = 30,000 manhours
Construction = 420,000 manhours
Those numbers are calculated from the resource loading.
Hours needed to finish certain quantity = Productivity Rate (Hour/Quantity) X Quantity
If we assumed that the total weight of the project will be 100,000 unit
So it’ll be distributed as follows:
Engineering = 100,700 / 550,700 * 100,000 = 18,286 units = 18.2%
Procurement = 30,000 / 550,700 * 100,000 = 5,448 units = 5.4%
Construction = 420,000 / 550,700 * 100,000 = 76,266 units = 76.4%
Check: 18,286 + 5,448 + 76,266 = 100,000 unit
So, in our example, the construction will have almost 75% of the weight, while the engineering has almost 20% and the rest 5% will be for the procurement activities.
Those 5% (5,448 units) will be distributed over the procurement activities with the same method.
That will maintain a good reflection of the complexity of your activities, and give you near-real progress percentages in your weekly and monthly updates.
Which will lead at the end to avoiding conflicts, delays, and misleading information in the reports/ dashboards.
This is a short video from our Youtube channel talking about calculating the progress % using the manhours and how it will be better than using cost.
To sum up this article in short sentences, it’s important to weigh your activities for better monitoring of your activities.
This weight can be based on duration, cost, complexity level, experience level, and resource hours needed. Whatever the method you will use, here is how to implement it in your time schedule How to calculate Planned % and Actual % using Weight.
Agree with your team and stakeholders on certain criteria from the beginning of the project to assure that your project will work seamlessly and to avoid any future problems in monitoring.
We created another article to show you how to calculate the planned and actual % of your activities using weight on Primavera P6
you can find it here: How to calculate Planned % and Actual % using Weight