Spindle centre's

I am installing new spindles as mentioned in other posts. The length down the pitch of the stairs is 2700mm betwwen newels and i need to use 18 spindles at 19mm wide. Could someone tell me the centres to drill my spindles at whilst trying to keep the spacing gaps the same.
I have researched different calculators but i am just getting confused. any help will be much appreciated.
Thanks

If I'm reading this correctly then you haven't got enough spindles, your spacing is coming out at about 125mm whereas legally it should be no more than 100mm so sprogs can't put their head through. ?Better still try to aim for less than 100mm.
22 spindles gives you a spacing fractionally below 100mm.

22 spindles at 19mm =418mm.
so this gives 22 spindles i.e 23 spaces.
run of the string = 2700mm
2700mm-418mm =2282mm
2282 divided by 23 = 99.2mm
don't forget your string is at an angle so the spindles are in effect slightly over 19mm where they seat so you may need to adjust this slightly.

The length of 2700mm is down the pitch not horizontally so would 18 spindles not be okay. i have 9 steps. What calculation do i need to do to get the centre's?

The important figure is that 100mm. Simplest thing to do is to measure a horizontal line and divide by 100, easiest way to measure this is by using the treads and a square.

you need to measure your spindle at the actual say 40% ANGLE and measure the coverage
you then need to aim for 95mm to allow the space to be less than a 100mm sphere can pass through
can you measure the distance horizontally ?? then we can go for spindle plus 95mm and an extra space

The distance horizontally is 2005mm

Ah it becomes clearer.
So using some of our original calculations-
18 spindles @ 19mm = 342mm or to put it another way 342mm of your space will be taken up with wood leaving you 1663mm of air to be divided up equally.
So 18 spindles needs 19 spaces which gives us a very presentable 87.5mm give or take a hundredeth of a mm.
If you mark your first spindle off the bottom newel using a square or short level you will be able to measure the distance along the top of the string (which will be something along the lines of what I first thought around 125)and cut a spacer to ensure accuratcy rather than trying to mark it all off the horizontal.
Hope we've cleared it all up for you now. If you are unsure mark everything out first in pencil before you pick up a drill or hammer.