Actually, you want to depress each string (or capo) at the 3rd fret and measure the clearance under the string at the 1st fret with feeler gauges.
Like I mentioned previously, there are various approaches and clearance preferences as different as the player themselves.
Also different manufacturers will state different specs. That said, as general starting point, the bass E should be between .008" - .010" and the treble E between .004" - .006". Again with graduated heights in between across the nut.
I will reiterate that these figures (and any set up specs really) are dependant on playing style; tuning type used (low C?????); string gauge; playing technique etc.
My method is a bit of a compromise of the graduated one outlined above. I break it into 3 "steps" E/A @ .008" - D/G @ .006" - B/E @ .004". This is just what I do and what works for me. YMMV.
Edit to add:
FWIW, I just checked a couple of my strats and the unfretted string height above the 3rd fret is ≤ .75mmI've heard that 2mm is a good height around the third fret...