Dry sand has an approximate density of 1.6Kg/L water is about 1Kg/L, so for every litre of volume you'll want 1.6Kg of sand to displace it.
0.8*0.35*0.05=0.014 m[sup]3[/sup] or 14 Litres, so you'll need 1.6*14L = 22.4Kg of sand approximately.
That can't be right, surely?
I bought two 15kg bags of the Argos playsand and it's done two four foot tanks, to a depth of one or two inches.
If it's nice weather where you are do it outside, it's much nicer; plus it's really hard to get all the sand out of the bath and it's not nice to sit on!
