Pea Gravel Calculator: How Much Do I Need?

This calculator tells you the volume of pea gravel you need to cover a rectangular area at a chosen depth, in both cubic feet and cubic yards. You enter the length and width of the space in feet, and the depth you want in inches; the calculator returns the volume of gravel required. It also gives you the cubic feet figure, which is handy if you plan to buy gravel in bags rather than by the cubic yard.

Formula

The calculator uses the basic volume formula for a rectangular prism:

Volume (cubic feet) = Length (ft) × Width (ft) × Depth (ft)

Since you enter depth in inches, you first convert it to feet by dividing by 12. Then to get cubic yards, you divide the cubic feet by 27 (because there are 27 cubic feet in a cubic yard). Combining both steps gives:

Volume (yd³) = (L × W × D) / 324

where:

• L = length of the area in feet (ft)
• W = width of the area in feet (ft)
• D = depth of gravel in inches (in)

The constant 324 comes from 27 (ft³ per yd³) × 12 (inches per foot).

Worked Example

Using the default values from the calculator: length = 40 ft, width = 25 ft, depth = 3 in.

1. Convert depth to feet: 3 in ÷ 12 = 0.25 ft
2. Calculate cubic feet: 40 × 25 × 0.25 = 250 ft³
3. Convert to cubic yards: 250 ÷ 27 = 9.26 yd³ (rounded to two decimals)

The calculator shows 9.26 yd³ and 250.0 ft³, matching the manual calculation.

Why Depth Matters

Pea gravel is usually spread 2–3 inches deep for walkways and patios. At 2 inches, a 10×10 ft area needs about 0.62 yd³; at 3 inches, it needs 0.93 yd³. For driveways, you might go 4 inches deep, and for drainage behind retaining walls, 6 inches or more. The calculator lets you adjust depth to see how much more material you need for each extra inch.

A common mistake is measuring the area in feet but the depth in inches and forgetting to convert. Another is mixing up cubic feet and cubic yards when ordering. Many suppliers sell gravel by the cubic yard, but bagged gravel is sold by cubic foot (typically 0.5 ft³ per bag). Always check which unit your supplier uses.

How to Measure Your Space

For a simple rectangle, measure length and width in feet. For irregular shapes, break the area into rectangles, calculate each one, and add them together. For a circle, use the formula π × r² (r = radius in feet) and then multiply by depth. The calculator works best for rectangular areas, but you can approximate odd shapes with a rectangle that covers the same footprint.

When measuring, use a tape measure and round up to the nearest foot. If your space is 12 ft 6 in long, use 13 ft to avoid underestimating. It’s always better to order a little extra (about 5–10%) to account for settling, compaction, and uneven ground.

Common Problems and Misconceptions

• Underestimating volume: People often forget that gravel settles. Freshly spread gravel compacts by about 10%, so your 3-inch layer may become 2.7 inches after a few weeks. Order extra to maintain the depth.
• Confusing weight and volume: Pea gravel is sold by volume (cubic yard), not weight, in most landscaping suppliers. Weight varies with moisture and stone size, so don’t rely on weight estimates.
• Assuming one bag covers a certain area: Bag coverage depends on bag size and depth. A 0.5 ft³ bag at 3 inches deep covers 2 square feet (0.5 ft³ ÷ 0.25 ft = 2 ft²). Always calculate based on volume.
• Forgetting the depth of the base: If you’re laying pea gravel over landscape fabric, the fabric doesn’t add depth. If you need a 4-inch layer, that’s 4 inches of gravel, not 4 inches including fabric.

Ordering and Delivery

When ordering bulk gravel, suppliers typically deliver by the cubic yard. A standard pickup truck holds about 1–2 cubic yards, but check with your supplier. Delivery fees often apply, and some suppliers require a minimum order. If you’re buying bags, calculate the number of bags by dividing the total cubic feet by the bag size (e.g., 250 ft³ ÷ 0.5 ft³ = 500 bags). That’s a lot of bags, so bulk delivery is usually more practical for large areas.

For a small project like a 5×5 ft walkway at 3 inches deep, you need 0.23 yd³ or 6.25 ft³. That’s about 13 bags of 0.5 ft³ each. For a 40×25 ft area, you’d need 500 bags—definitely order in bulk.

Alternatives and Comparisons

Pea gravel is one of many loose aggregates. Compare it with:

• Crushed stone: Angular pieces that lock together, better for driveways, but less comfortable to walk on barefoot.
• River rock: Larger, smoother stones, often used for decorative beds, but harder to walk on and more expensive.
• Sand: Fine and compact, but washes away easily and doesn’t drain as well.
• Mulch: Organic, decomposes, needs replacement, but is cheaper and better for planting beds.

Pea gravel is popular for paths, play areas, and around plants because it’s smooth, drains well, and doesn’t decompose. However, it can shift underfoot and may need edging to stay in place.

Frequently Asked Questions

How many bags of pea gravel do I need?

Divide the total cubic feet you need by the cubic feet per bag. For example, if you need 250 ft³ and each bag is 0.5 ft³, you need 500 bags. Always round up to the nearest whole bag.

How deep should pea gravel be?

For walkways and patios, 2–3 inches is typical. For driveways, 4 inches or more. For drainage applications, 6 inches or more. The calculator lets you adjust depth to see the volume difference.

What area does a cubic yard of pea gravel cover?

At 3 inches deep, one cubic yard covers 108 square feet (27 ft³ ÷ 0.25 ft = 108 ft²). At 2 inches, it covers 162 ft²; at 4 inches, 81 ft².

How much does a cubic yard of pea gravel weigh?

Pea gravel typically weighs about 1.4–1.7 tons per cubic yard, but this varies with moisture and stone size. Weight is not needed for ordering by volume, but it matters for transport and structural calculations.

Can I use pea gravel for a driveway?

Yes, but it’s not ideal because the smooth stones shift under vehicle weight. Crushed stone is better for driveways. If you use pea gravel, you’ll need a thicker layer and regular maintenance.

How do I calculate for a circular area?

Measure the radius (half the diameter) in feet, square it, multiply by π (3.14159), then multiply by the depth in feet. For example, a 10-ft diameter circle at 3 in deep: radius = 5 ft, area = 78.54 ft², volume = 78.54 × 0.25 = 19.64 ft³ = 0.73 yd³.

Related

• Lawn Edging Calculator: Pieces and Stakes
• Paver Base Calculator: Gravel Base and Bedding Sand
• Topsoil Calculator: Cubic Yards and Tons

in l | Lawn length | ft | 40 | 0 | 100000
in w | Lawn width | ft | 25 | 0 | 100000
in d | Depth | in | 3 | 0 | 120
out yd | Volume | yd³ | l * w * d / 324 | 2
out ft3 | Volume | ft³ | l * w * d / 12 | 1