# Cost Estimating Power Rule



## udpolo15

I am trying to scale a cost down from an estimate that has twice the capacity that is needed. (for a waste water treatment package plant). The cost/relationship isn't linear and I seem to recall a power rule you can use to scale the cost down (6/10 power rule or something like that). Can anybody point me in the right direction?


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## Guest

^^^ I remember that too - specifically with respect to sizing/costing WWTP unit operations. My recollection was that it was a formula/algorithm more than just a factor (power) because I took an Environmental Analysis class years ago that focused on optimization methods and some of the build-design cost scaling was based on linear programming.

I am out of town until the end of the week, I will check my notes when I get back to my office.

Regards,

JR


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## Guest

Okay, the so-called 0.6 power rule works as follows:

Cost (Q) = Cost (Q0) * (Q/Q0)n

Such that:

Cost (Q) = construction cost, $million

Q = design flow, mgd

Q0 = base design flow based on another reference

n = emperical scaling factor (assumed to be 0.6)

FWIW - I found a document that suggests the value for n falls more between 0.80 and 0.85. You can find the document that includes construction cost data at Full Scale Design and Cost Estimate Peer Review Report

I hope this helps.

Regards,

JR


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## rudy

see p. 16 for "six tenths rule" or "rule of 0.6"

http://www.calvin.edu/academic/engineering...finalreport.pdf


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## udpolo15

Thanks! This is what I was looking for.


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