The largest ones I ever raised reached 10-12cm, not counting fin extensions. Counting finnage is a poor way of measuring. The linebred ones that are often in stores have artificially selected fin length, so they are 'bigger'. With fins in, I can see 5 inches as possible, but only as a rare size. Around 4 seemed standard. I kept and raised many of them over several years. I tended to see pairs after they bred, and not see how big they eventually got. Most were sold at 3 inches maximum.
They push the limits of what a dwarf cichlid is supposed to be. It took a few years for my breeder males to get there. The largest I had was the only linebred I ever kept. My wild sourced ones and the fry I raised never got to his size. I saw the same with veijita.
I think in metric, but I had a tape measure with both systems sitting on the kitchen counter.
