This is a fairly unfamiliar approach/equation for processing qPCR data.  The units can apparently end up as ng/uL or some unit of Molarity (e.g., picomolar or nanomolar, etc.) - if one assumes that the "Mean-Q" value is unit-less.  But, rather than Mean-Q (which I assume means 'mean relative quantity'), in qPCR, one needs rather to use the geometric mean of the relative quantity values to appropriately correspond to the Cq values from which the 'Q' values came.  Can you elaborate more on how your Mean-Q values were calculated?  Use "ng" and "uL" throughout this equation - and you will see what I mean. A few minutes in Excel or with pen and paper can help you patiently work through this.  I like the equation, and realize that it is perhaps the product of previous work in the field of sedimentology, but, there are more orthodox ways of representing the variables in the equation that would be more readily amenable to the usual vernacular in the qPCR world proper.  What is the efficiency of amplification of your qPCReaction(s)? Have you proven lack of sample-related inhibition of the qPCR, do you run standard curves, what do you use for standards, etc.?  Are you familiar with the transformations: EAMP = 10(-1/slope) and  Relative quantity or Xo = EAMP(b-Cq) and so on...

Relative quantity or [relatively] absolute # of copies of target DNA sequence per gram of sediment would seem to acceptable final units to express your data in. 

But, without further details as to how you actually carry out your qPCR, what the target (or targets are), how you measure your input DNA, etc., would need to be spelled out more here in order for the outsider to get a better grip on what you are actually doing.

i understood your questions, i followed already the proper steps, incase we are use Biorad instrument, no need to calculate manually, they have the option for automated calculation once we feed our data, how much volume and quantity of DNA we use like, incase we use ABI PRISM , we have to calculate manually, so that am doing for manual calculation, if we took the CT value from the instrument, and we can add our sample measurement, what kind of unit we have to follow, because its depends on mass/volume, while we do for the environmental sample we reduce the concentration of DNA sample, from original extraction. and the original extraction we measured in ng/µl.  but if we reduced the concentration we dilute the sample in 1- 20 or 1-10 dilution. and preparing the reaction we use the 25µl, total volume of reaction on that time also the final concentration is changing. and the sediment sample we took from gram unit. so that means, its MASS/Volume. this is my major confusion to make proper calculation. and what kind of common unit to follow all data. is it any other formula have for sediment sample qPCR calculation to find the environmental abundance.

Umapathy,

What is your qPCR target in the DNA extracted from the sediment samples?  And what is the volume of [extracted diluted DNA] sample that you add to each 25 uL qPCReaction?

 The attached paper here is a very good example of how to achieve your aims.

My target to find the microbial abundance from this qPCR analysis, am using the cbbM Gene, for finding the marine carbon fixation bacterial abundance. and am used 0.3g of sediment to extract the DNA using Fast prep method, finally we collect 80µl template DNA. in this template i use for the PCR reaction 1-20 dilution, and am use 4µl of diluted DNA for reaction, the total reaction volume is 25µl.,  my proper question is need the calculation FORMULA for finding the microbial abundance and FINAL UNIT for commonly using the data. 

The attached file here should give you what you need. Read through it carefully.

Number of bacterium/gram sediment is the most user-friendly final unit. 

Thank you very much, i will go through it with my original data.

the answer is extensively discussed in youtube >>with examples .. search in youtube