Going with (compare) pics.. lol
...
Gonna try my best here -
Px4 full size - just a tad longer in both length and grip length than P228/229 series guns shown below
Px4 Compact (rotating barrel) aprox same size as Sig P228/229 series
Px4 Sc smallest Px4 they make and is out in 9mm (but only with tilt-up barrel action)
Now the pics:
Full size Px4 and Sig P228
Smaller, Px4 Compact aprox same size as P228/229 series guns
Below - Count the number of serrations vs full size above along with length of rail also noting that they come with slide/lock release levers on "both" sides and others, top and at bottom only have one on the left side.
Compact model with rotating barrel:
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Now count and look at difference between Compact above and Sc below (the smallest (again, no rotating barrel below)
Below - this is an Sc 9mm model compared to an SA EMP 1911 SAO 9mm, 9+1
Smallest Px4Sc with tilt-up barrel-action
The big difference between all of them vs the last one shown, the tiny Sc model is the grip.. All have full, natural, grips and the Px4 Sc 9mm, one needs a Pinkie extension to get/have a full grip.. (just too small a gun IMO, and it's fat)
OMMV,
Ls