Sandbox Sand Calculator

How much sand a sandbox holds

Sand is sold by weight or by volume, but a sandbox is sized by its footprint and how deep you want the sand. The job is to turn those three numbers, length, width and depth, into cubic feet, then into pounds and bags.

Two facts make the conversion easy. Dry play sand weighs about 100 pounds per cubic foot, and a standard 50 pound bag holds about 0.5 cubic feet. So every cubic foot of sandbox is about 100 pounds, or two bags of play sand.

The depth is the number people guess at. A sandbox that looks half full at 3 inches leaves little room to dig, and a sandbox filled to the rim spills over the sides. A working depth of 6 to 9 inches covers most play, and deeper sand is needed if the sandbox sits under a slide or climber. The calculator above handles any shape and any depth, and it flags the depth against the safety guidance.

The formula: length times width times depth

For a square or rectangular sandbox, the volume in cubic feet is length times width times depth, with depth written in feet. Since sandbox depth is usually given in inches, divide the inches by 12 first.

• Step 1: measure the inside length and width in feet
• Step 2: convert the depth to feet, so 6 inches becomes 0.5 feet and 9 inches becomes 0.75 feet
• Step 3: multiply length times width times depth to get cubic feet
• Step 4: multiply cubic feet by 100 to get pounds, then divide by 50 for bags

For a round sandbox, measure the diameter and use the area of a circle, which is pi times the radius squared. A 5 foot round sandbox has a radius of 2.5 feet, an area of about 19.6 square feet, and at 6 inches deep it holds about 9.8 cubic feet of sand, or roughly 980 pounds.

Round up to the next whole bag when you buy. Sand settles and compacts after a few weeks, so having half a bag on hand to top off the box is useful.

Worked example: a 4 by 4 foot sandbox at 6 inches

Take a common 4 by 4 foot sandbox and fill it to 6 inches.

• Volume: 4 times 4 times 0.5 = 8 cubic feet
• Weight: 8 times 100 = 800 pounds
• Bags: 800 divided by 50 = 16 bags of 50 pound play sand
• In cubic yards: 8 divided by 27 = about 0.30 cubic yards

If you buy in bulk, 0.30 cubic yards is the number to give the landscape yard. If you buy bags, 16 is the count. At $6 a bag that is about $96 of sand, and you may want one extra bag for top-ups, so budget for 17.

Now push the depth to 9 inches, which is what the CPSC wants when the sandbox sits under equipment. The volume becomes 4 times 4 times 0.75, which is 12 cubic feet, or 1,200 pounds, or 24 bags. The sand nearly doubles in weight and cost, which is why the depth decision matters before you buy. A shallow box that is only meant for digging can stay at 6 inches and save half the sand.

Sand volume, weight and bags by sandbox size

This table covers the sandbox sizes sold most often, at two working depths. The bag count uses 50 pound bags of play sand.

Weight adds up fast. A 4 by 8 sandbox at 9 inches holds more than a ton of sand, which is why the frame needs to be built for the load. Set the calculator above to your own dimensions if your box is a different size.

How deep should sandbox sand be?

Depth is a safety question when the sandbox sits under play equipment. The Consumer Product Safety Commission treats sand as a loose-fill surface that cushions falls, and its guidance ties the depth to the fall height. Nine inches of sand protects against a fall from up to 4 feet, and the CPSC says never to maintain less than 9 inches of loose-fill material under equipment. The full numbers are in the CPSC Public Playground Safety Handbook.

For a home sandbox used only for digging and building, with no climbing structure over it, 6 to 9 inches is a practical working depth. Kids dig down to the bottom quickly, so anything under 4 inches gets frustrating. Anything over about 8 inches in a small box can spill over the sides and track into the house.

If you are placing a slide or a climber, keep it on its own protective surface and do not count on the sandbox sand unless it is at least 9 inches deep and kept that way. Sand compacts and blows away over time, so check the depth each season. North Dakota State University Extension has a guide to playground surfacing depths that lists sand alongside wood chips and pea gravel.

Play sand versus builder's sand, and upkeep

The sand you choose matters as much as how much you buy. Play sand is washed and screened, which removes fine dust and sharp particles, and its grains are rounded so they feel soft and pack well for building. Builder's sand and paver sand are crushed, dusty and often angular, and the fine crystalline silica in that dust is a breathing hazard for children and adults. Do not use construction sand or fill dirt in a play area.

Once the sand is in, a little upkeep keeps it usable.

• Cover it. A lid or a fitted tarp keeps out rain, leaves and animals. Cats treat an open sandbox as a litter box, which is the biggest contamination risk.
• Rake weekly. Turning the sand over lets it dry and brings debris to the surface, where you can pull it out.
• Top it up. Sand compacts and blows away, so plan to add a bag or two each season to hold the depth.
• Replace when dirty. If the sand is fouled by animals or soaked repeatedly, replacing it is the safe move.

A base layer of landscape fabric under the sand keeps weeds and burrowing animals out and stops the sand from mixing with the soil. Use a fabric that drains so water does not pool, and build the frame to hold the weight of the sand you calculated above.