Gravel and Rock Calculator: How Much You Need

A gravel and rock calculator works out the volume and weight of stone you need for a project, based on the area you want to cover and the depth you plan to use. You enter the length, width, and depth of the space, and the calculator returns the volume in cubic yards or cubic meters, plus the estimated tons or kilograms of material. This helps you order the right amount from a supplier, avoid overpaying for excess, and prevent running short mid-project.

Formula

The core formula is simple: Volume = Length × Width × Depth, where all measurements are in the same unit. For gravel, depth is usually given in inches, so you convert it to feet by dividing by 12. The weight is then Weight = Volume × Density, where density is the mass per unit volume of the specific rock type.

• L = length of the area (ft or m)
• W = width of the area (ft or m)
• D = depth of the gravel layer (in or cm)
• V = volume (ft³ or m³)
• Ï� = density of the gravel (lb/ft³ or kg/m³)
• M = mass/weight (lb, tons, or kg)

To convert cubic feet to cubic yards, divide by 27 (since 1 yard = 3 feet, and 3³ = 27). To convert tons (short tons) to pounds, multiply by 2,000.

Worked Example

Using the default values from the calculator above: length = 20 ft, width = 10 ft, depth = 4 in, density = 105 lb/ft³.

1. Convert depth to feet: 4 in ÷ 12 = 0.333 ft
2. Calculate volume in cubic feet: 20 × 10 × 0.333 = 66.6 ft³
3. Convert to cubic yards: 66.6 ÷ 27 = 2.47 yd³
4. Calculate weight: 66.6 × 105 = 6,993 lb
5. Convert to tons: 6,993 ÷ 2,000 = 3.50 tons

The calculator rounds the volume to 2.5 yd³ and the weight to 3.5 tons, matching the example.

Why Depth Matters More Than You Think

Most people underestimate how much gravel they need because they focus on area, not depth. A 10×10 ft patio at 2 inches deep needs about 0.62 cubic yards, but at 4 inches it jumps to 1.23 cubic yards – double the material. The depth you choose depends on the purpose:

• 2-3 inches – decorative mulch or light walkway covering
• 4 inches – standard driveway or parking area (with proper base)
• 6 inches or more – heavy vehicle traffic or poor soil conditions

Always compact the gravel after spreading, which reduces volume by about 10-15%. If you plan to compact, add that extra to your order.

Density: Not All Gravel Weighs the Same

The density of gravel varies significantly by type and moisture content. Common values (dry, loose):

• Pea gravel – 95-105 lb/ft³
• Crushed stone (limestone) – 100-110 lb/ft³
• River rock – 100-120 lb/ft³
• Decomposed granite – 105-125 lb/ft³

Wet gravel can weigh 10-15% more. If you’re ordering by weight, ask your supplier for the exact density they use. Many suppliers sell by the ton, not the cubic yard, so knowing the density is critical for an accurate order.

Common Mistakes and How to Avoid Them

Even with a calculator, people make errors. Here are the most frequent ones:

• Mixing units – entering length in feet and width in yards. Always convert everything to the same unit first.
• Forgetting to convert depth – depth is usually in inches, but the formula needs feet. Divide by 12.
• Ignoring compaction – if you compact, you’ll need about 10% more than the loose volume.
• Ordering by volume vs weight – suppliers often charge by the ton, so know the density.
• Not accounting for irregular shapes – for circular areas, use Ï€r²; for odd shapes, break into rectangles and add them.

For a circular area, the formula becomes Ï€ × (radius)² × depth. For a triangle, it’s 0.5 × base × height × depth.

How to Measure Your Space Accurately

Getting the dimensions right is half the battle. Use these tips:

1. Use a tape measure or laser measure for straight lines. For curves, use a flexible measuring tape or a piece of string.
2. For irregular areas, divide into rectangles, triangles, and circles. Calculate each separately, then sum.
3. Measure depth at several points – the ground may be uneven. Average the depths.
4. Add 5-10% extra for waste, spillage, and settling. This is especially important if you’re doing a curved edge or have obstacles.

If you’re covering a driveway that slopes, measure the average depth across the slope, not just at the top or bottom.

Cost Considerations (Without Specific Prices)

Gravel is typically sold by the cubic yard or by the ton. The price per ton varies by region, type, and delivery distance. To estimate cost, multiply the weight (tons) by the local price per ton. Delivery fees are often separate, and minimum order quantities may apply.

Buying in bulk is almost always cheaper per unit than buying in bags. A 0.5 cubic foot bag of pea gravel covers about 2 square feet at 3 inches deep. A full cubic yard covers about 108 square feet at 3 inches deep – that’s 54 bags. The cost difference is significant, so for any area larger than a few square feet, bulk delivery is the better option.

Frequently Asked Questions

How many square feet does a ton of gravel cover?

It depends on depth. A ton of gravel (about 20 cubic feet at 100 lb/ft³) covers 80 square feet at 3 inches deep, 60 square feet at 4 inches, or 40 square feet at 6 inches. Use the calculator with your depth to get an exact number.

What’s the difference between crushed stone and pea gravel?

Crushed stone is angular, made by crushing larger rocks, and locks together when compacted – good for driveways and bases. Pea gravel is naturally rounded, smaller (about 3/8 inch), and shifts more easily – better for walkways and decorative areas. The density is similar, but the application differs.

Should I order by cubic yard or by ton?

Order by ton if your supplier sells by weight, which most do. To convert, multiply the cubic yards by the density (in lb/ft³) and divide by 2,000. For example, 2.5 yd³ at 105 lb/ft³ = 2.5 × 27 × 105 / 2000 = 3.54 tons. Always confirm the density with your supplier.

How much gravel do I need for a 10×10 shed base?

For a shed base, you typically want 4-6 inches of compacted gravel. At 4 inches, you need 10×10×(4/12) = 33.3 ft³ = 1.23 yd³. At 6 inches, it’s 1.85 yd³. Add 10% for compaction loss, so order about 1.4 or 2.0 yd³ respectively.

Can I use the calculator for river rock or boulders?

Yes, but adjust the density. River rock is heavier (around 110-120 lb/ft³) and boulders are sold by weight, not volume. For boulders, measure the approximate volume (length × width × height) and multiply by the density to get weight, but note that irregular shapes have significant void space – you may need to add 20-30% for gaps.

What if my area is an L-shape or has a curve?

Break the L-shape into two rectangles, calculate each, and add. For a curve, approximate it as a series of straight segments or use a circle formula if it’s a perfect arc. When in doubt, add 10% extra – it’s cheaper to have a little left over than to order more and pay a second delivery fee.

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in length | Length | ft | 20 | 0
in width | Width | ft | 10 | 0
in depth | Depth | in | 4 | 0
in density | Density | lb/ft³ | 105 | 0
out volume_ft | Volume | ft³ | length * width * (depth / 12) | 1
out volume_yd | Volume | yd³ | (length * width * (depth / 12)) / 27 | 1
out weight_lb | Weight | lb | volume_ft * density | 0
out weight_tons | Weight | tons | (volume_ft * density) / 2000 | 1