How much coir to add to soil???

I have 8 bags of soil that does not have any coir in it. Im wanting to add coir, So does anybody have any idea on how much to add to 8 bags worth? 1.5 cubic feet per bag so around 12 cubic ft total so i was thinking of adding around 2 cubic ft of the coir, but i dont know if thats to much or not enough.
Yep, Im making the SS recipe but couldnt find any soil w/coir, well i could have but couldnt pay the extra $300 just for the shipping.
Please help me out if you can.
Thanks
BigBudE

It is really up to you...I try to aim for coir being about 25 to 33 percent of the mix. In your case that would be from three to four cubic feet.

I have used up to 50% in my mixes, but lately I am using 25%. You can't mess anything up with the stuff, its inert.

Peace

i usually add a 5 kilo block to 3 or 4 bags of potting soil with my medium.