How much does an eyelash weigh?

Based on experiment done by someone for fun, 80 micrograms is two eyelashes - so one eyelash (on average) would be 40 micrograms.

For comparison ten grains of sugar weigh around 750 micrograms, i.e. a single grain of sugar (on average) weighs 75 micrograms.

Of course YMMV - but this should at least give you a rough number for estimation purposes.