See if this makes sense once you've read through it:
((1/(1+(1.000696)^(-((XS*.333))-.5)*2000000)+25*B
Where B is the number of power blocks in the entire ship, and XS is what you get when you add the following for every generator (collection of connected power blocks) in the ship:
Xn = (Nn/3)^1.7. For each generator, Nn is the width + height + length in blocks of the generator*. If you have some number of generators with the exact same dimensions, you can remember that the sum of all of their Xn values would be the number of generators with identical Nn values multiplied by their (also identical) Xn value.
* You want the actual dimensions. If it curves back on itself like a snake but is only three blocks wide at its widest, you're using 3 for the width.
XS = sum of all Xn
And the equation that you put XS into again is
((1/(1+(1.000696)^(-XS*.333))-.5)*2000000)+25*B
So if you just have one ship with ten 1x1x200 generators and a 25x25x25 cube, you could do the 25x25x25 cube like this:
X0 = (N0/3)^1.7, where N0 = (25+25+25), so X0 = 237.956742339
and then one 200-length generator as X1, and just add it to XS 10 times (multiply by ten).
X1 = (N1/3)^1.7, where N1 = (200+1+1), so X1 = 1282.30458472
XS = X0 + 10*X1 = 13061.0025895
To calculate B (total number of power blocks), just multiply the block dimensions together. 200x1x1 generators are 200 blocks each, and the 25x25x25 is going to be 25*25*25. With ten of the 200x1x1s, B will be:
B = 200*10 + 25*25*25 = 17625
Now to solve the final equation:
((1/(1+(1.000696)^(-((XS*.333))-.5)*2000000)+25*B
Plug in the values we calculated:
((1/(1+(1.000696)^(-13061.0025895*.333))-.5)*2000000)+25*17625
Result: 1,348,101.12242
Note that the result may be slightly different from what starmade gives, despite using the exact same equations, particularly for numbers in the millions or above. Might be due to using different precision data types? Hard to say.
P.S. I used google's calculator this time, but if you do this in a spreadsheet or the like, you're much less likely to make a mistake. I had to double check everything after I noted that the result was too low, as I had made several mistakes, likely due to being quite tired. What I mean is, you can set it up to have number of generators, width, height, and length fields, and take from those to generate values that it automatically plugs into formulas to generate a result for you. Then you only have to worry about getting the equations and math right once.