Your sandbox needs about 10.0 cubic feet (0.370 cubic yards) of sand.
That weighs roughly 1000 lb (453.6 kg), which is 20 standard 50-lb bags.
The 5 in (preschooler preset) fill depth is the standard recommendation for preschoolers (3-5 years).
At the price you entered, budgeting roughly $160.00 covers the material cost.
Buy 5-10% extra to account for settling and spillage. Play sand is non-toxic and safe for children; avoid construction sand, which may contain silica dust.
Next stepFor a rectangular or square sandbox, the area is length times width. Always check manufacturer coverage labels, since bag capacities can vary slightly.