How Much Play Sand for a Sandbox?

Kids need depth, not a dusting

A sandbox that is 2 inches full is a dusting, not a dig pit. Quikrete’s Play Sand table plans 4, 6, and 8 inch fills for boxed play — this site’s 8-inch worked example matches that manufacturer table. That is not CPSC fall-zone surfacing: Publication 325 uses 9 inches of compressed sand for a 4-foot playground fall height. Keep the box walls taller than the sand so the first week of play stays inside.^{27, 28}

The volume formula is the same as topsoil: cubic yards = length × width × depth in inches ÷ 324. A common 4 × 4 box at 8 inches is 4 × 4 × 8 ÷ 324 = 0.4 cubic yards, about 0.5 tons. A 6 × 6 box at 8 inches is 0.9 yards, about 1.2 tons.

Bag counts are Quikrete’s published 50 lb Play Sand table (each bag ≈ ½ cubic foot). Yards use NIST ÷ 324; tons use this site’s 1.35 planning factor. The sand calculator’s bag line is 2-cubic-foot bags, so use this table for play-sand sacks.^{27, 1}

Bags versus a scoop

Quikrete sells Play Sand in 50-pound bags of about ½ cubic foot. Their table is 21 bags for a 4 × 4 at 8 inches and 48 bags for a 6 × 6 at 8 inches. The larger box is a trailer or a bulk scoop. Landscape yards and some farm stores will sell a half-yard of play sand if you ask; not every “sand” pile is play-grade, so say the word “play.”²⁷

The sand calculator’s bag count uses 2-cubic-foot bags, the same unit as the topsoil tool. Play-sand bags are usually smaller. Use the yard number as the source of truth and convert with the bag size on the package.

What not to pour in

Mason sand is fine and can pack into a crust. Concrete sand is coarse on skin. Fill sand may contain silt and rock. Beach sand you drove home may be salty and may not be something you want in a closed backyard box. Buy material sold as play sand.

Put a landscape fabric or a drained base under the box so the sand does not vanish into the lawn, and so water does not sit. A sealed plastic liner with no drain is how you get a swamp.

Covers and refresh

A cover keeps cats out and rain from washing fines away. Even with a cover you will lose sand over a season. Budget a few bags each spring rather than another half-yard. If the sand smells or stays wet, replace it; do not just add a fresh layer on top of a problem.

Round boxes and odd kits

A round plastic turtle-lid box is a circle. Use the sand calculator’s circle mode with the inside diameter and 6 to 8 inches of depth. A 5-foot-diameter box at 8 inches is about 0.5 yards (π × 2.5² × 8 ÷ 324). Measure inside; the advertised “5-foot” box may be outside the lip.

Wooden kits with benches steal floor area. Measure the sand floor, not the outer timber. If the bench hangs over the sand, children will still kick sand out; keep 2 inches of freeboard.