This beans test got me thinking.
When I bought them I measured my Magadan bags l x w x h as you would a rigid box and got 24L, similar to my calcs on Siskiyous (see earlier).
But the other day I managed to fill one with no less than 40 litres of water in the waterproof liner, roll it all up and clip the bag shut.
So I've learned something new: a cube is different, but the dimensions of a flexible suitcase-shaped
box (aka: soft moto pannier) cannot be compared with a rigid box of the same size.
That is something to think about if comparing hard vs soft volumes by dimensions alone.
There's more here