The Gravel Calculator Math That Saves You From Two Trips to the Supply Yard

Most homeowners ordering gravel for the first time buy the wrong amount — usually short, occasionally embarrassingly over. A gravel calculator fixes that in 30 seconds, but only if you understand what goes into the formula and why depth is the number that controls everything else.

Here is the calculation method, the real-world numbers for the most common projects, and exactly how to use them.

How the Gravel Calculator Formula Works

The core formula converts your project dimensions into the two numbers suppliers actually use: cubic yards and tons.

Step 1 — Cubic feet:  Length (ft) × Width (ft) × Depth (ft)
Step 2 — Cubic yards: Cubic feet ÷ 27
Step 3 — Tons:        Cubic yards × 1.35  (crushed gravel at 2,700 lbs/yd³)

Pea gravel runs lighter — approximately 2,600 lbs per cubic yard, or a multiplier of 1.30. Gravel mixed with sand runs heavier at roughly 3,240 lbs per cubic yard, or a multiplier of 1.62. The type of material you order changes the tonnage even when the volume stays the same.

Worked example — a 10 ft × 20 ft area at 4-inch depth:

• Cubic feet: 10 × 20 × 0.333 = 66.7 ft³
• Cubic yards: 66.7 ÷ 27 = 2.5 yd³
• Tons (crushed gravel): 2.5 × 1.35 = 3.3 tons

That is the basic engine behind every gravel calculator for cubic feet, yards, and tons. The inputs are simple. The depth variable is where most people make the error.

The Number That Actually Controls Your Order

Depth is not a minor input. Doubling depth doubles your material order — and most project types have a correct depth range that is non-negotiable.

Standard single-car driveway (12 ft × 40 ft) — crushed gravel at 2,700 lbs/yd³:

The difference between a 4-inch and a 6-inch driveway on a 12 × 40 ft surface is 4 tons of material. Get the depth wrong and you either under-build or you are paying to haul away excess gravel.

For residential driveways handling regular passenger vehicles, 4 to 6 inches of compacted gravel is the standard specification. Areas expecting heavier vehicles or trucks should run 6 to 8 inches.

Calculate your gravel yards, cubic feet, and tons instantly →

Depth Requirements by Project Type

Getting the volume right starts with knowing what depth your project actually requires. These are standard specifications, not minimums to cut.

Driveways (crushed gravel or #57 stone):

• Residential passenger vehicles — 4 to 6 inches compacted
• Frequent truck or RV traffic — 6 to 8 inches compacted
• Commercial or heavy equipment — 10 to 12 inches

Walkways and landscape gravel:

• Decorative coverage only — 2 to 3 inches
• High-foot-traffic paths — 3 to 4 inches

Retaining walls (drainage gravel behind the wall):

• Gravel should extend vertically behind the wall as a continuous drainage column
• Minimum 6 inches of 3/4-inch to 1-1/2-inch clean drain rock
• Foundation-level retaining walls may require 24 to 36 inches of drainage gravel depth to relieve hydrostatic pressure

French drains (gravel-filled trenches with perforated pipe):

• Standard residential trench: 12 inches deep × 10 to 12 inches wide
• Gravel must fully surround the pipe — 3 inches beneath, 3 inches above, and packed to each side
• A 50-foot French drain at 12-inch depth and 10-inch width requires approximately 2.6 cubic yards of 3/4-inch washed drain rock

Pea gravel works well for decorative applications, walkways, and playground surfaces. For French drains and driveways, use angular crushed stone — pea gravel's round shape does not compact and will not hold under vehicle loads or pipe pressure.

The Overage Rule and Why It Exists

Every gravel calculator gives you a volume based on perfect geometry. Real ground is not a perfect rectangle. Gravel also compacts after delivery — loose material typically reduces 10 to 20% in volume once spread and settled.

Order 10% more than your calculated number for any project. On a 5.9 yd³ driveway calculation, that means ordering 6.5 yd³. On a 2.5 yd³ patio calculation, order 2.8 yd³. The cost of a partial extra yard is a fraction of the cost of a second delivery.

Suppliers sell by the cubic yard or by the ton. Confirm which unit your quote is in before ordering. A quote of "$45 per yard" and "$45 per ton" on the same material is a meaningful price difference when 1 cubic yard of dense gravel weighs 1.35 tons.

Frequently Asked Questions

How do you calculate how much gravel you need?

Multiply length × width × depth (all in feet) to get cubic feet, then divide by 27 to get cubic yards. Multiply cubic yards by 1.35 for crushed gravel or 1.30 for pea gravel to get tons. A 10 × 20 ft area at 4-inch depth requires 2.5 cubic yards or 3.3 tons of standard crushed gravel. Add 10% to any result to account for compaction and settling.

How many cubic yards of gravel do I need for a standard driveway?

A single-car driveway at 12 ft wide × 40 ft long built to the standard 4-inch residential depth requires 5.9 cubic yards, or 8.0 tons of crushed gravel. At 6-inch depth the same driveway needs 8.9 cubic yards and 12.0 tons. Most suppliers require a minimum order of 1 to 3 cubic yards for delivery.

Should I use pea gravel or crushed stone for a driveway?

Crushed stone — typically #57 stone or crusher run — is the correct material for driveways that carry vehicle traffic. Its angular edges interlock under compaction, forming a stable surface. Pea gravel's smooth, rounded shape does not compact and shifts under tire loads, creating ruts. Pea gravel is the right choice for walkways, patios, decorative beds, and landscaping where foot traffic is the primary load.

What is the correct gravel depth for a French drain?

A standard residential French drain trench runs 12 inches deep and 10 to 12 inches wide. Gravel — 3/4-inch washed angular stone — fills the trench and must surround the perforated pipe with at least 3 inches on all sides. A 50-foot French drain requires approximately 2.6 cubic yards of drain rock. For French drains behind retaining walls, depth requirements increase significantly, often reaching 24 to 36 inches to properly relieve hydrostatic pressure behind the wall.

How does gravel type affect how many tons I need to order?

Density varies by material. Standard crushed gravel weighs approximately 2,700 lbs per cubic yard, so 1 yd³ equals 1.35 tons. Pea gravel runs lighter at around 2,600 lbs per cubic yard, or 1.30 tons. Gravel mixed with sand is heavier — approximately 3,240 lbs per cubic yard, or 1.62 tons. Ordering by cubic yards controls volume. Ordering by tons controls weight. Confirm which unit your supplier quotes before placing an order to avoid receiving less material than your project requires.