Or do you just take a best estimate and risk being slightly over weight?
In doing so you also risk invalidating the permit the insurance and your livelyhood!
but any regulation regime which requires pilots and passengers to look like anorexics and carry only enough baggage to brush their teeth and only enough fuel for a single circuit is absolutely barmy.
The UK microlight definition was originally 340 Kgs and was a weight below which, regulation did not apply! In order to improve undercarriage and braking systems the weight was raised to 450Kgs which then resulted in better, higher performance aircraft, rather than the proposed modifications.