Hi Dale,
I don't actually measure ratios, I just add a bit at a time until it clumps together... A little on the drier side is safer than too wet.
They can tolerate quite a range of moisture levels. I usually start out with vermiculite that is damp to the touch and towards the end when they are about to hatch I make it much more moist to simulate spring rains and such. I also boost the temps at the same time.
Sorry that isn't too specific but I hope it helps.