Take a known volume container, say you have a box of 30 x 30 x 30 cm = 27000 Cm3 or 27 Liters or 0.027 Cum.
Take the weight of empty box and not down its weight say 1 kg
Fill the box with sand without compacting it and weight it and record the weight, say it comes to - 45.55 Kg
So the weight of sand will be - 44.55 Kg
Volume of sand will be - 0.027 cum
So the density of sand will be - weight / Volume = 44.55 / 0.027 = 1650 kg/cum.
Now you have the density of sand (mostly its called as dry loose bulk density)
Now understand the relation
1 cum = 35.32 cft
so if you want to convert it to cft then you need to divide it with 35.32
So you get sand density = 1650 / 35.32 = 46.71 Kg/cft
No measure your sand volume at site in cft and multiply it with above density per cft.
say you have 100 cft sand at site - so its total weight will be = 46.71 x 100 = 4671 Kg.
You can use any size and shape box of known measurement for calculation of density.