A sandbox needs more sand than most people expect. This calculator works out the volume, the weight and the number of bags for a square, rectangular or round sandbox, plus the frame and cover sizes.
How deep?
Fill a sandbox 6 to 12 in deep. Less and children hit the bottom when they dig; more is costly and hard to rake. About 8 in is a good default for young children.
Volume and weight
volume = length × width × depth (in feet)
For a round sandbox, the area is π × diameter² ÷ 4.
A 6 × 6 ft sandbox filled 8 in deep holds 36 × 8 ÷ 12 = 24 cubic feet. Dry play sand weighs about 100 lb per cubic foot, so that is 2,400 lb, or 48 bags of 50 lb. Damp sand weighs more, and a bag of sand settles, so buying a bag or two extra is wise.
Play sand is often sold in 50 lb bags at home centers; for very large sandboxes, bulk delivery by the cubic yard is cheaper (1 cubic yard is 27 cu ft).
Choosing the sand
- Use sand labeled as play sand, washed and screened to remove silt and sharp debris.
- Avoid construction sand, which can be dusty and stain clothes.
- Some sands made from crushed quartz create fine dust. Look for products tested for low crystalline silica, or choose natural washed sand, and dampen it slightly if it is dusty.
Frame and base
The frame length is the perimeter, 24 ft for a 6 × 6 ft box. Use untreated cedar or other rot-resistant wood, or a plastic kit, and add a ledge or corner seats. At the bottom, lay landscape fabric: it lets rain drain away while keeping weeds and soil out of the sand. A layer of gravel under the fabric helps on clay soils.
Cover
Cover the sandbox when it is not in use to keep out rain, leaves and especially cats. A tarp, mesh cover or hinged lid works. The calculator sizes the cover with 1 ft of overhang on each side, 8 × 8 ft for the example.
Maintenance
Rake the sand regularly to remove debris, let it dry in the sun, and top it up each spring, since sand spills out as children play. Replace it completely if it becomes soiled.