# how to calculate manhours

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hi guys,

this is my first query how to calculate man hours per drawing. whether based on size(a1,a2,a3,a4) , or by based on drawing.. some companies they are calculating based on sheet size...

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Calculate manhours based on sheet size? What if you are drawing a house floor plan versus a complete fabrication drawing for a K. Bedford Tenkara racing bike and the sheet size is the same for both?

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Calculate manhours based on sheet size? What if you are drawing a house floor plan versus a complete fabrication drawing for a K. Bedford Tenkara racing bike and the sheet size is the same for both?

thks for responding.. its based on a vessel drawing,skid and platform drg.(mechanical)

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ReMark said it best, it all depends on what you're calculating manhours for. Every discipline does it differently. Most of the time, estimators simply throw a percentage of the total contract price in for drawings...but again..it all depends on the scope of work.

I've been in estimating for many years and what I can tell you is that labor, no matter which end you're looking at, is the most intangible item to put a cost on. It not only depends on the scope of work but also many outside factors which you're not allowed or condoned to accomodate for like inclement weather, or something as intangible as did your detailers go out drinking at a topless bar last night. Many things affect the amount of time it takes to get drawings (the work) completed. And labor is always a crap shoot.

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A vessel drawing? OK. Let me ask....

What is the size of the vessel in gallons/liters?

What type of head is being used at the top and bottom?

How many nozzles will there be and what are their sizes?

How many manways will there be and what are their sizes?

Will there be any legs on this vessel? If so, how many and what size will they be?

Legs: type? Pipe, structural shape, other?

Will there be any baffles?

Will the vessel have any bayonets or internal coils?

Will the vessel be jacketed? If so will it be a dimple jacket or a half-pipe?

Will the vessel have any special features that will have to be included as part of the design?

What is the diameter of said vessel? What is the straight side length?

How many lifting lugs will be required and where will they be located?

Those are just some of the questions I could come up with. So, think about it. You could have two similar sized vessels but one could be used as a storage tank and the other as a reactor and their complexity will vary greatly. Yet, each could have to be drawn on the same size sheet. Which do you think would take more time?

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A vessel drawing? OK. Let me ask....

What is the size of the vessel in gallons/liters?

What type of head is being used at the top and bottom?

How many nozzles will there be and what are their sizes?

How many manways will there be and what are their sizes?

Will there be any legs on this vessel? If so, how many and what size will they be?

Legs: type? Pipe, structural shape, other?

Will there be any baffles?

Will the vessel have any bayonets or internal coils?

Will the vessel be jacketed? If so will it be a dimple jacket or a half-pipe?

Will the vessel have any special features that will have to be included as part of the design?

What is the diameter of said vessel? What is the straight side length?

How many lifting lugs will be required and where will they be located?

Those are just some of the questions I could come up with. So, think about it. You could have two similar sized vessels but one could be used as a storage tank and the other as a reactor and their complexity will vary greatly. Yet, each could have to be drawn on the same size sheet. Which do you think would take more time?

it is reactor which takes more time for detailing than tank....

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"...it is reactor which takes more time for detailing than tank..."

In light of that statement then don't you think using sheet size as a means of estimating manhours would be inappropriate?

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Sheet size is irrelevant. Estimating how much to quote for a job just comes with experience. Sometimes you under quote or the job goes over budget and you take a loss.

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thanks for all, i want to know how they (project managers) are calculating engineering man hours thats y i asked(process design+design+drafting+checking). if any other views pl. tell me.

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Probably based upon past projects they tracked.

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Sheet size is irrelevant. Estimating how much to quote for a job just comes with experience. Sometimes you under quote or the job goes over budget and you take a loss.

Sometimes as in some of the time....sheesh. If I had a nickel for everytime...well you know the routine.

The point is that labor, be it engineering calculations, drawings, shop labor and mostly field installation labor, is always an intangible thing. One can only make educated guesses at it and that's where experience comes in. Not to say that you couldn't use something like a per sheet method of calucluation time to determine costs. As a PM I often ask the detailers how many sheets they plan on making for a project and we try to determine costs as well as schedules from there. The problem is that they almost always run over the amount of time it takes and new sheets which either weren't accounted for or could not have been accounted for crop up. That's why my preferred method of estimating engineering/drafting is to add a percentage of the budget to the line items, usually anywhere from 5% to 12%. But like I said, I have seldom seen a time when engineering and drawings came in under budget. Remember the old saying and this is just as true now as it was thousands of years ago when they were building the pyramids:

Engineering is a necessary evil. If you think it's expensive with it, try building something without it.

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