How do you calculate wingloading

Wing loading is the aircraft's weight divided by the wing area.
And it's expressed in oz/sq.ft (imperial) or g/sq.dm (metric) in aircraft modelling context.

we use grains per furlong sqd.

Hey Dick,

That's a new one, it's really amazing how we keep learning every day...
I recall somebody from the Far West who used pennyweight per acre for the sake of accuracy.

The desire for extreme accuracy is ongoing-------

Yeah sure, however, striving for extreme accuracy may also become a non-productive obsession.
But as someone once said, it's always preferable to calculate almost right than exactly wrong…

probably right----------

To quote an old stand up comic....

Wha'da bunch of chameleons!