My old T used to ask me every session how suicidal I was on a scale of 1-10. I usually run from a 6.5-8.5 though I have hit a 10 before at my lowest (not too long ago). There is no set-in-stone indicator by which I gauge this, but how I usually assess is based on whether I have a plan and whether I feel compelled to carry it out. The latter part is key because I always have many plans running through my head (I mentally device a possible suicide scenario from every item/place I see) but at about 9 I'll have settled on a singular one and begin to need to do it. This is when the rational/self-preserving/sane voice gets drowned out by the chorus of bloodthirsty ones.