Gravel Calculator Triangle: Volume & Cost

A gravel calculator for a triangular area works out the volume of gravel needed to fill a triangular-shaped space (such as a garden bed, path corner, or driveway apron) and often the total cost based on price per unit. You enter the triangle’s base, height, and desired gravel depth, and the calculator returns the volume in cubic feet or cubic meters, plus the number of tons or bags required. This tool is essential for ordering the right amount of gravel—avoiding both costly over-ordering and inconvenient shortages.

Formula

The volume of gravel for a triangular area is calculated using the area of a triangle and the desired depth:

• Area of the triangle = (Base × Height) / 2
• Volume = Area × Depth

In symbols: V = (B × H / 2) × D

Where:

• B = base length of the triangle (in feet or meters)
• H = height of the triangle, measured perpendicular to the base (in the same unit)
• D = depth of the gravel layer (converted to the same unit as B and H)
• V = volume of gravel needed (cubic feet or cubic meters)

To convert volume to weight, multiply by the gravel’s density. A common average density for gravel is about 1.4 tons per cubic yard (or roughly 1.68 tons per cubic meter). For the calculator above, we use 1.4 tons per cubic yard, which is a typical value for crushed stone.

Worked Example

Let’s use the default values from the calculator: base = 10 ft, height = 6 ft, depth = 3 inches, price = $40 per ton.

1. Calculate the area: (10 ft × 6 ft) / 2 = 30 ft²
2. Convert depth to feet: 3 inches ÷ 12 = 0.25 ft
3. Calculate volume: 30 ft² × 0.25 ft = 7.5 ft³
4. Convert to cubic yards: 7.5 ft³ ÷ 27 = 0.278 yd³
5. Convert to tons: 0.278 yd³ × 1.4 tons/yd³ = 0.389 tons (about 778 pounds)
6. Calculate cost: 0.389 tons × $40/ton = $15.56

The calculator shows a volume of 7.50 ft³, 0.39 tons, and an estimated cost of $15.56. This matches the manual calculation.

When to Use a Triangular Gravel Calculator

Triangular gravel areas are common in landscaping and construction. You might need to fill:

• A triangular garden bed or planter
• A wedge-shaped area between a driveway and a walkway
• A corner of a yard for a patio or seating area
• A triangular drainage swale or ditch
• A decorative rock garden with angled borders

In each case, the same formula applies: measure the base and height of the triangle, decide on the gravel depth, and compute the volume. This calculator simplifies the math, ensuring you order the right amount.

How to Measure a Triangular Area

Accurate measurements are crucial for a correct estimate. Follow these steps:

1. Identify the base: Choose one side of the triangle as the base. It can be any side, but the longest side often works best.
2. Measure the base: Use a tape measure to get the length of the base in feet or meters.
3. Find the height: The height is the perpendicular distance from the base to the opposite vertex (the highest point). Use a tape measure or a laser distance measurer to get this distance.
4. Determine the depth: Decide how deep you want the gravel layer. Common depths are 2–4 inches for walkways, 4–6 inches for driveways (though this often includes a base layer), and 1–2 inches for decorative ground cover.
5. Input the values: Enter the base, height, and depth into the calculator.

If your area is not a perfect triangle, break it into smaller triangles and rectangles, calculate each separately, and add the volumes.

Common Mistakes and How to Avoid Them

Several errors can lead to incorrect gravel estimates:

• Using the wrong height: The height must be perpendicular to the base, not the length of the slanted side. Measure straight down from the apex to the base.
• Unit mix-ups: Ensure all measurements are in the same unit. If you measure the base in feet and the depth in inches, convert the depth to feet (divide by 12) before multiplying.
• Forgetting to divide by 2: The area of a triangle is half the base times the height. Skipping this step doubles your volume.
• Ignoring compaction: Gravel compacts when spread and tamped. Order about 10% extra to account for settling, especially for driveways.
• Assuming all gravel weighs the same: Density varies by material. Pea gravel is lighter than crushed stone. Check with your supplier for the exact density if you need precise tonnage.

Gravel Types and Density

The density of gravel affects the weight and thus the number of tons you need. Common types include:

• Pea gravel: Small, rounded stones, often used for playgrounds and paths. Density around 1.2–1.4 tons per cubic yard.
• Crushed stone: Angular pieces, good for driveways and drainage. Density around 1.4–1.6 tons per cubic yard.
• River rock: Smooth, larger stones, used decoratively. Density around 1.5–1.7 tons per cubic yard.
• Bank gravel: A mix of sand and gravel, often used as a base. Density around 1.4–1.5 tons per cubic yard.

If you know the exact density of your gravel, you can adjust the calculator’s weight factor. For most DIY projects, 1.4 tons per cubic yard is a safe average.

Frequently Asked Questions

How do I calculate gravel for a triangle without a calculator?

Use the formula: Volume = (Base × Height / 2) × Depth. Measure the base and height in feet, convert the depth to feet (divide inches by 12), multiply, and you get cubic feet. Divide by 27 to get cubic yards, then multiply by the gravel density (about 1.4 tons per cubic yard) to get tons.

What depth of gravel do I need for a walkway?

For a residential walkway, a depth of 2–3 inches of gravel is typical. If the walkway will support heavy foot traffic or wheelbarrows, go with 3–4 inches. For a driveway, you’ll need 4–6 inches of compacted gravel, often with a larger base layer.

How many bags of gravel do I need?

Bags of gravel are typically sold in 0.5 cubic foot or 1 cubic foot sizes. Divide your total volume in cubic feet by the bag size. For example, a 7.5 ft³ volume would need 15 bags of 0.5 ft³ each. Bags are convenient for small projects but are more expensive per cubic yard than bulk delivery.

Can I use this calculator for other shapes?

No, this calculator is specifically for triangular areas. For rectangular areas, use a simple length × width × depth formula. For circular areas, use π × radius² × depth. If you have an irregular shape, break it into triangles and rectangles, calculate each, and sum the volumes.

How much extra gravel should I order?

It’s wise to order 5–10% extra to account for compaction, spillage, and uneven ground. For driveways where compaction is significant, add 10–15%. For decorative ground cover, 5% is usually enough. This ensures you don’t run short and have to make a second trip.

What if my triangle is not right-angled?

The formula works for any triangle, not just right-angled ones. You just need the base and the perpendicular height. Even if the triangle is obtuse or acute, the area is still half the base times the height. Measure the height from the apex straight down to the base line, even if the apex is not directly above the base.

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in b | Base | ft | 10 | 0
in h | Height | ft | 6 | 0
in d | Depth | in | 3 | 0
in p | Price per ton | $ | 40 | 0
out v | Volume | ft³ | (b * h / 2) * (d / 12) | 2
out tons | Gravel needed | tons | v * 1.4 | 2
out cost | Estimated cost | $ | tons * p | 2