Rules of Thumb for estimating design effort

[71corvette]

Not sure this is quite the right forum, but I'll give it a shot...

I’m looking for some quick “gut check” type rules-of-thumb for estimating engineering design effort on projects. I recognize that a proposed fee needs to be based on the estimated effort to complete a given scope of work, but what about coming up with a quick estimate of effort?

Do you use percentage of construction cost?
Do you base it on number of plan sheets expected?
How do you separate preliminary design effort from the final design effort?

Thanks for your thoughts!

 

[Qshake]

In the heavy infrastructure market, it is not uncommon to see numbers in the 10-15% range of construction costs for design fee with 5% being preliminary and the remainder final design, detailing, & specifications.

The higher the costs, the less the percentage....say 6-8% of construction costs.

I've seen estimates broken down into sheets, if they are well defined.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[IRstuff]

Your best bet is to maintain detailed historical records, from which you can draw from later. Unfortunately, no one does that, even though that's the best practice.

But, the basic idea is that if you know what scope you did in the past and the amount of workd involved, you can ratio a new proposal's scope, and roughly determine an estimated cost.

In aerospace, it's often found that the initial bottom's up bid was the most correct, and that the "scrubbing" that ensues generally degrades the verisimilitude of that original bid.

TTFN

FAQ731-376

 

[GregLamberson]

71corvette

Qshake's advice is probably as good as you are going to get. Allot of the answer depends on the complexity of the project. The only danger in using a % mark up is that on a simple project with say a huge pipe order, it could be skewed somewhat. But then again, if you are looking at some order of magnitude shot at it, a % will get you there - in oil & gas projects, we typcially see engineering costs at 5%-10% of TIC. If you see much above 15%, I would start looking for a reason.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[ajack1]

In my experience the real issue is the state of the market place, just as with stocks and shares and house prices the price you might have got last year has little to do with what you might get today.

Even a range of 5-10% is a huge difference and would probably see you coming in as the cheapest or the most expensive.

Just out of interest, in structural work would you actually know the price of the project to quote design against? This is rarely the case in automotive.

 

[KENAT]

In mechanical there are various methods based on how many drawings, what size of drawing, number of pages and complexity of components beign drawn. However that's more the design documentation side than the actual design, project management etc. Also with the advent of CAD, especially 3D, it's of arguably less relevance.

KENAT, probably the least qualified checker you'll ever meet...

 

[SKIAK]

This wouldn't help you right away, but the firm I work for keeps spreadsheets and graphs of projects and total final costs. They range from squarefootge and pounds of steel to number of sheets and details. Really helpful to get a real quick idea. Else I would agree with Qshake.

 

[Twoballcane]

May be repost this in "Starting and Running an Engineering Company"

http://www.eng-tips.com/threadminder.cfm?pid=784

They should have some good ideas....


Tobalcane
"If you avoid failure, you also avoid success."

 

[dougantholz]

In the midwest we are used to seeing less than 1% for structural design fees based on a white box finish. You can also estimate your man hours and use a multiplier (say 2.5 time salary) and you can use a per sheet cost (say $4,000 per sheet). You can also use a $$/sq ft if you know the construction type and final use. For instance in the building market you might use 70-80 cents/sf for office space, but 10-15 cents for warehouses. There's also a size divisor (1M sf warehouse won't have the same per square ft fee as a 40,000 sf warehouse).
Of course not all projects are created equal and rules of thumb are only about as accurate as using your thumb to measure the pyramids - so be careful. As always, run it by management

 

[71corvette]

Interesting feedback guys, thanks for the tips!