Sandbox Sand Calculator (kg of play sand & bags to buy)

Understanding the sandbox sand calculator — concept and principle

This calculator works out how much play sand a square, rectangular or round sandbox needs, by volume and weight, and how many bags to buy. Parents, schools and nurseries use it before filling a new sandbox or topping up an old one.

Box volume × sand density: with the default inputs the result is 24 bags (of 20 kg).

How it is calculated

Floor area: rectangle = length × width; circle = π × (d ÷ 2)².
Volume (m³) = area × sand depth (cm³ ÷ 1,000,000).
Weight (kg) = volume × bulk density.
Bags = weight ÷ bag size, rounded up.
Litres = m³ × 1,000; ft³ = m³ ÷ 0.0283168.

The principle

Sand fills the sandbox like water fills a container, so its volume is floor area times depth. Sand is sold by weight, so volume is converted with the bulk density, which includes the air between grains. Loose dry sand is roughly 1,500–1,700 kg/m³; damp sand is heavier. The default 1,600 kg/m³ is an example; the bag or supplier figure is better when available.

Worked example

Default inputs: square 120 × 120 cm, depth 20 cm, density 1,600 kg/m³, 20 kg bags.

Area = 1.2 × 1.2 = 1.44 m².
Volume = 1.44 × 0.20 = 0.288 m³ = 288 L = 10.2 ft³.
Weight = 0.288 × 1,600 = 461 kg.
Bags = 460.8 ÷ 20 = 23.04, rounded up to 24.

Each point is the calculator re-run with only “Length or diameter (cm)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Length or diameter (cm)	Sand needed (kg)
30	115
60	230
90	346
120	461
150	576
180	691
240	922

How to read the result

Fill to a few centimetres below the rim so the sand stays in the box. A depth of around 20 cm lets children dig without hitting the bottom. Sand settles and gets carried out on clothes, so expect to top up each season.

Common mistakes

Using the outside dimensions of the frame instead of the inside.
Buying builders' sand, which can stain and contain sharp grains.
Forgetting a lining under the sand to keep out weeds and soil.
Underestimating the weight when carrying bags.

Keep in mind: Use sand sold for children's play. Cover the sandbox when not in use to keep animals out.

Frequently asked questions

How much sand for a 120 × 120 cm sandbox?

About 0.29 m³, or 461 kg, at 20 cm deep: 24 bags of 20 kg.

How deep should sandbox sand be?

Around 20 cm is a common choice for digging; fill a few centimetres below the rim.

How much does a cubic metre of sand weigh?

Loose dry sand is roughly 1,500–1,700 kg.

Sources: NIST Special Publication 811 (2008), Appendix B (1 ft³ = 0.028316846592 m³)

Checked 9 Nov 2026. Geometry (box and cylinder volume) and mass = volume × bulk density; 1 ft³ = 0.028316846592 m³ (exact). The sand density default is an example value — use the figure on your product.

Your numbers