Interesting question. However, does thing belong to H.SE?

@KentaroTomono Considering the Swiss guard is centuries old, this does in fact seem to be a history question.

@CMonsour Okay. ^^

If they need to as tall as 6.8, every Swiss Guards can consist of a good basketball team. lol. Sorry.

I have talked to Swiss Guards some 40 years ago and I can assure you they were nor 6’8” in the slighted.

@KenGraham What about 400 years ago? Or more?

It's likely that there were some who were that tall, but unlikely that that was the requirement, especially 400+ years ago.

i know that napoleon's personal guard were picked for their height, but 6'8" does seem a very high bar for those days. Even now few people are that tall.

Could not find anything ad-hoc on the Swiss Guard's requirements when formed. I looked for "Gardemaß" (literally, "guard's measure", the common German term for "minimum height requirement for guards of honor"); something that's in my mind affixed to "six feet". Indeed there's for example the Potsdam Giants ("Lange Kerls"), with 6 Prussian feet minimum height (that's 6'2" imperial for you, or 1.88m). A 6'8" / 2.03m requirement, 500 years ago, would have meant they could not have fielded an effective fighting force, which they were originally...

(ctd.) ...because they became an honor guard only later (and gigantism usually reduces athletic ability). So, while I have no proof on this, I'd daresay that if there was a minimum height requirement originally, it would have been much lower, and probably secondary to actually fielding an effective unit. (Even the Potsdam Giants, for which I could source a height requirement, did fill their ranks with smaller recruits.

the body of teh question states 5'8" I assume this is the correct one?

For comparison, only about 25% of current NCAA male basketball players - 1355 men - are 6'8" or over. Considering that they're drawn not just from the current 300 million plus population of the US, but potentially other countries, vs the current 8.42 million population of Switzerland (and that the potential of an NBA career is vastly more rewarding than that of mercenary soldier), it seems highly unlikely that there were enough people over 6'8" to form the Swiss Guard.

And remember the Swiss Guard was originally a mercenary army, which was only later reformed into a largely (but not entirely) ceremonial group. Even with a requirement of 5'8" they'd have had trouble getting enough recruits to maintain a reasonable size force on the battlefield.

Would any of these measures have ever been given in Imperial units, as the question implies?

@Orangesandlemons Vatican website says 174 cm vatican.va/roman_curia/swiss_guard/swissguard/ammissione_en.‌​htm

@jwenting To clarify, I am asking about the Swiss Guard at the Vatican, not about the Swiss mercenary army.

@JonathanCender they're one and the same. The Swiss Guard was the Swiss mercenary army, until those became part of the Swiss national armed forces, and is now drawn from those.