How Much Sand for a Sandbox? Calculator & Buying Guide

The math for a sandbox is quick — length times width times depth — but there are a few decisions that matter more than the math. What kind of sand is actually safe for kids? How deep does it need to be? When should you replace it? This guide covers all of it, along with a quick-reference table so you can skip straight to your sandbox size and know exactly how many bags to buy.

How Much Sand by Sandbox Size

The table below shows sand needed at two common fill depths — 4 inches for younger kids and 6 inches for active digging play. Numbers are in cubic feet, then converted to standard 50 lb bags of play sand (each bag covers about 0.9–1 cubic foot).

The formula is simple: Length (ft) × Width (ft) × Depth (ft) = cubic feet. Convert depth to feet first (4 inches = 0.33 ft, 6 inches = 0.5 ft). Divide by 0.9 to get the number of 50 lb bags.

Sand Calculator

For an odd-shaped or custom-size sandbox, use the calculator below. Set your depth to 4 or 6 inches and enter your sandbox dimensions.

What Kind of Sand Is Safe for a Sandbox?

This matters more than the quantity math. Not all sand is the same, and the difference between play sand and construction sand isn't just marketing — it's a legitimate safety distinction.

Use: Washed Play Sand

Play sand is specifically processed for children's use: washed to remove debris, graded to a consistent fine grain size, and tested for safety. Look for bags labeled "play sand" or "sandbox sand" — the wording matters. It's widely available at any home improvement store, hardware store, or garden center, and it's what 50 lb bags of play sand at most retailers contain. Buying locally is almost always cheaper than shipping — check your nearest Home Depot, Lowe's, or farm supply store for comparable pricing before ordering online.

Avoid: Construction Sand, All-Purpose Sand, and Industrial Sand

Here's the concern: many sands — especially industrial silica sand and unprocessed construction sand — contain crystalline silica (quartz). In adults, prolonged occupational exposure to crystalline silica dust causes silicosis, a serious lung disease. The risk from occasional backyard play is orders of magnitude lower than industrial exposure, but the key word in "play sand" is that it's been processed to reduce fine silica dust — the particle size and wetting behavior are different.

The practical rule: if the bag says "play sand" or "sandbox sand" and is marketed for children, you're fine. If it says "all-purpose sand," "fill sand," "washed concrete sand," or doesn't mention children at all, skip it for a sandbox.

How Deep Should You Fill a Sandbox?

Depth affects both the play experience and how quickly sand gets depleted as kids dig and throw it out.

For a standard store-bought sandbox kit — the kind with a molded plastic base — 4 inches is usually right. For a built sandbox with 6-inch sides, fill to 6 inches so kids can dig to the bottom without hitting wood.

Bags vs. Bulk: When Does Bulk Make Sense?

Play sand at a hardware store runs about $5–$8 per 50 lb bag, which covers roughly 0.9 cubic feet. Bulk play sand from a landscape supplier runs $30–$50 per cubic yard (27 cubic feet). Bulk starts making sense at roughly 10–15 cubic feet if you can do local pickup — delivery fees often cancel the savings at smaller volumes.

The main variable is delivery. If you have a pickup truck and a local landscape supplier carries washed play sand in bulk (call ahead to confirm it's play-grade, not construction sand), bulk is usually cheaper above about 15 cubic feet. Below that, bags from a nearby hardware store are more convenient and not significantly more expensive.

Should You Put Landscape Fabric Under the Sandbox?

Yes, with one caveat. A layer of weed barrier fabric under the sandbox does two things: keeps weeds from growing up through the sand, and prevents the sand from mixing into the soil over time (which means less topping off). Use a permeable landscape fabric — not plastic sheeting — so water drains out rather than turning the sandbox into a puddle.

The caveat: if your sandbox is a molded plastic kit with a solid bottom, it already handles both issues and fabric isn't needed. For wooden sandboxes and custom builds with open bottoms, fabric is worth the $10–$15 it costs.

Covering the Sandbox

A cover is one of those things that seems optional until you realize your sandbox has become a neighborhood cat toilet. Uncovered sand outside also collects rainwater, leaf debris, and insects. A properly fitted sandbox cover keeps the sand clean between uses, extends how long the sand stays usable, and is the single most effective way to slow down how often you need to replace it.

When to Replace Sandbox Sand

Well-maintained sandbox sand lasts 1–2 years with regular covering. Signs it's time to replace it:

• Color change: Sand that was light tan has turned gray or dark — usually from organic debris mixing in.
• Odor: Any smell beyond neutral or slightly earthy means organic material is decomposing in the sand.
• Clumping that won't dry out: Normal damp clumping from rain dries out in a day or two. Persistent clumping means the sand has too much organic content or debris.
• Animal waste:If a cat (or anything else) has been using the sandbox, replace the sand. Washing it isn't sufficient.

To maximize sand life: cover it consistently, rake out debris every few weeks, and let it dry fully after rain before covering again.

Sandbox Kits vs. Building Your Own

A sandbox kit is the quickest path — most kits include the frame, a cover, and sometimes a small amount of sand. They work well for young kids and small spaces. The trade-offs: molded plastic kits are shallower (limiting how much sand fits), and the plastic degrades in UV over 3–5 years.

A DIY wooden sandbox — cedar or pressure-treated 2×8s or 2×10s screwed into a frame — is deeper, more durable, and customizable to whatever size fits your yard. Cedar is the best wood choice for outdoor contact with kids (no chemical treatment concerns). A 4×6 ft cedar sandbox costs roughly $60–$100 in lumber, plus sand.

Related Calculators

• Sand Calculator — for paver bedding, pool bases, and all other sand projects
• How Much Sand Do I Need? — full sand depth guide for every project type
• Raised Bed Calculator— if you're also building a garden bed nearby, calculate your soil fill in the same session