Quantitative Guidelines for thickness of TIM/heatsink coumpound

I apologise for posting this as it has probably been answered many times in many places previously. But I am unable to find the kind of answer I'm looking for.

How thick is the layer of thermal grease / heatsink compound / thermal interface material (TIM) between a CPU and a heatsink (made this century) is effective ? I'd like some NUMBERS here.

I realise it "depends", therefore please mention the circumstances that apply; give a range if you feel that is more appropriate than a single number, e.g. 0.01 thou to 0.08 thou (of an inch). I do not know the typical roughness and parallelism of the CPU 'heatspreader' (as Intel call the metal case which forms the top part of a CPU package) nor of a typical heatsink sold for this purpose, but the thickness of TIM must be greater than this ?

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12.Aust.2015