Gravel Calculator for Garden: How Much You Need

A gravel calculator for a garden works out the volume and weight of gravel you need to cover a given area at a chosen depth. You enter the length, width, and desired depth of the bed, and it returns the volume in cubic feet or cubic meters, plus the weight in tons or kilograms based on the gravel density you select. This lets you order the right amount in one go, avoiding both shortfalls and expensive over-delivery.

Formula

The core formula is simple: Volume = Length × Width × Depth. For a rectangular garden bed, measure the length and width in the same unit (feet or meters), then multiply by the depth you want the gravel layer to be. Because depth is usually given in inches while length and width are in feet, convert the depth to feet first by dividing by 12. The result is the volume in cubic feet. To get cubic yards, divide by 27 (since 1 cubic yard = 27 cubic feet).

Weight is then volume × density. Gravel density varies by type and moisture content, but typical values are around 1.4 to 1.7 tonnes per cubic meter (or 90–110 lb per cubic foot). The calculator uses a density in tons per cubic yard, which is the common way gravel is sold in the US. For example, pea gravel is about 1.68 tons per cubic yard, while crushed stone is closer to 1.60 tons per cubic yard. The formula for weight in tons is: Weight (tons) = Volume (cu ft) × Density (tons/cu yd) / 27.

Worked Example

Using the default values from the calculator above: a garden bed 20 feet long, 10 feet wide, with a 2-inch gravel layer.

1. Convert depth to feet: 2 in ÷ 12 = 0.1667 ft.
2. Calculate volume in cubic feet: 20 × 10 × 0.1667 = 33.3 cu ft.
3. Convert to cubic yards: 33.3 ÷ 27 = 1.23 cu yd.
4. Calculate weight (using pea gravel density 1.68 tons/cu yd): 33.3 × 1.68 / 27 = 2.07 tons.

So for a 20×10 ft bed at 2 inches deep, you need about 1.23 cubic yards or 2.1 tons of pea gravel. The calculator rounds the weight to two decimals, giving 2.07 tons.

Why Depth Matters More Than You Think

Most garden gravel projects fail because the layer is too thin. A 1-inch layer will shift, expose soil, and let weeds through. For a path that gets foot traffic, aim for 2–3 inches of gravel. For a driveway that cars drive on, you need 4–6 inches, often with a base layer of larger crushed stone. For decorative beds where nothing walks on it, 2 inches is usually enough to look solid. The calculator lets you test different depths to see how much extra material each inch adds—going from 2 to 3 inches increases the volume by 50%.

Choosing the Right Gravel Type

Not all gravel is the same. The main choices are:

• Pea gravel: Small, rounded stones (about 3/8 inch). Comfortable to walk on, good for paths and play areas, but it shifts easily and needs edging.
• Crushed stone: Angular pieces that lock together. Better for driveways and areas that need stability. Available in various sizes from 1/4 inch to 2 inches.
• Bank run or river gravel: A mix of sizes, often with sand. Cheap but less uniform.
• Limestone or granite: Decorative options that come in different colors. Heavier and often more expensive.

The density in the calculator accounts for these differences. If you are unsure, ask your supplier for the density of the specific gravel they sell—it is usually listed on the product page or you can ask. Using the wrong density can change the weight by 10–15%, which matters when ordering by the ton.

Common Mistakes and How to Avoid Them

The biggest error is mixing units. If you measure length in feet but width in meters, the volume will be off by a factor of 10. Always use the same unit for all dimensions. Another common mistake is forgetting to convert depth from inches to feet—a 2-inch layer is not 2 feet. Also, gravel settles over time, so order about 10% extra to account for compaction and spillage. Finally, remember that weight is an estimate; wet gravel weighs more than dry. If you are ordering by the ton, tell the supplier you want a specific volume, and they will convert it using their own density.

How to Measure Irregular Garden Beds

Not every bed is a perfect rectangle. For L-shaped or curved areas, break the space into rectangles, calculate each one, and add the volumes together. For a circular bed, use the formula π × radius² for the area, then multiply by depth. For a triangular bed, use 0.5 × base × height for the area. The calculator works for any shape as long as you can find the area in square feet. If the area is truly irregular, a rough estimate is fine—gravel is forgiving, and you can always add more later.

Costs and Ordering Tips

Gravel is sold by the cubic yard or by the ton. In the US, a cubic yard of gravel typically weighs 1.4–1.7 tons, so a ton is roughly 0.6–0.7 cubic yards. Prices vary widely by region and type, but a common range is $15–$50 per ton for bulk gravel, with decorative types at the higher end. Delivery fees often apply, and some suppliers have a minimum order (like 1 or 2 tons). Use the calculator to get the volume, then call three local suppliers for quotes. Ask if they deliver and whether the price includes delivery. Also ask about the gravel’s compaction factor—some suppliers recommend ordering 10–15% extra because the gravel settles.

Alternatives to Gravel for Garden Beds

If gravel isn’t right for your project, consider these options:

• Mulch: Organic, cheaper, and better for soil moisture, but needs replacing every year or two.
• River rock: Larger, smoother stones that stay put better than pea gravel, but more expensive.
• Decomposed granite: Fine, compactable material that forms a hard surface, good for paths.
• Rubber mulch: Made from recycled tires, long-lasting, but can retain heat.
• Stepping stones or pavers: For paths, a solid surface may be easier to maintain than loose gravel.

Each has different maintenance needs and costs, so weigh the trade-offs before ordering.

Frequently Asked Questions

How deep should gravel be for a garden path?

For a path that people walk on, 2–3 inches is the sweet spot. Less than 2 inches will expose soil and let weeds through. More than 3 inches is wasteful unless you have a driveway or need a very stable base.

How many square feet does a ton of gravel cover?

It depends on depth. A ton of gravel (about 0.6–0.7 cubic yards) covers roughly 100–120 square feet at 2 inches deep, 70–80 square feet at 3 inches, and 50–60 square feet at 4 inches. Use the calculator to get an exact number for your specific depth and gravel type.

Should I put landscape fabric under gravel?

Yes, in most cases. Landscape fabric prevents weeds from growing up through the gravel and keeps the gravel from sinking into the soil. Use a heavy-duty woven fabric and overlap seams by at least 6 inches. Skip it if you want to grow plants through the gravel, but then you’ll have more weed maintenance.

How do I calculate gravel for a circular area?

Measure the radius (half the diameter) in feet, square it, multiply by Ï€ (3.1416), and you get the area in square feet. Then multiply by the depth (in feet) to get the volume. For example, a 10-foot-diameter circle has a radius of 5 ft, so the area is 3.1416 × 5² = 78.5 sq ft. At 2 inches deep, that’s 78.5 × 0.1667 = 13.1 cu ft.

Can I use the calculator for a driveway?

Yes, but you’ll need a deeper layer—usually 4–6 inches of crushed stone. Enter the length and width of the driveway, set the depth to 4 or 6 inches, and choose a crushed stone density. Keep in mind that driveways often need a base layer of larger stone, which you should calculate separately.

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in l | Length | ft | 20 | 0
in w | Width | ft | 10 | 0
in d | Depth | in | 2 | 0
sel density | Gravel type | Pea gravel=1.68, Crushed stone=1.60, Bank run=1.75, Limestone=1.55
out volume_ft3 | Volume | cu ft | l * w * (d / 12) | 1
out volume_yd3 | Volume | cu yd | (l * w * (d / 12)) / 27 | 2
out weight_tons | Weight | tons | (l * w * (d / 12)) * density / 2000 | 2