calculate project weight by cost

Kamyar,
it is a lot in function of the company for which you are working.
I saw different company allocating the weight different.
It depennd in which area the fell stronger.

Kamyar,

I work for an EPC company as well and this is how weight is usually distributed on the three phases (Engineering, Procurement, and Construction).

For Engineering, % wtg is distributed according to the ENGINEERING MANHOURS needed to produce different engineering documents. This is usually given to you by the different engineering disciplines, and it is your job as a planner to allocate these manhours and distribute them along the engineering phase of your schedule.

For Procurement , weightage is relatively easier to calcuate here since it is based on COST. Basically the more expensive materials / equipment will have a greater % wtg then the less expensive ones.

For construction, weightage is based on QUANTITIES.
Mechanical equipments will be in Tons
Structural Steel will be in Tons of Steel
Concrete pouring will be in m3 concrete.
Electrical and instrument cables will be in Lm
Excavation will be in m3
etc....

there are many many quantities. These quantities should than be transformed into CONSTRUCTION MANHOURS which is done by multiplying by production rates. example: hrs/m3, hrs/ton of steel, etc... These production rate are available here on the plannig planet site. just go to the Prod-rates section. After you’ve got your construction mnhrs ready you have to convert that to % wtg. Roughly the activities with the larger construction mnhrs (aka larger quantities) will have the larger weight factors.

Commissioning I believe is done like construction, but you should check on that cause i’m not sure.

I hope this helped.

Good luck,

Randa

Do you weight your WBS items by their duration? Can you share when you will use "duration" as the weight basis?

No i dont use duration for weight % because it will cause some problem,example: in some activity such as maintenance activities that they have long duration & low weight value Vs. construction works.