Guesstimates required because:
1. No official figures were promulgated for AUW of exfil troops complete with war kit, weapons and whatever other interesting items they had.
2. No air movements terminals on the small patches of bulldozed and oiled sand where the above could be weighed to within a sixteenth of an ounce (we were still in Imperial units back then).
3. We needed to get the job done, engines running and with a minimum of fannying about.
As I recall from my refugee/humanitarian sorties elsewhere, our passengers tended to be a bit lighter than the average British infantryman and were less prone to carrying honking great bergens and other big bags of stuff that goes bang. The non-SF folks also usually operated from a paved surface rather than an ad-hoc bit of desert which had been cleared as a strip.