Rock Calculator – Free Gravel, River Rock & Stone Calculator

Calculate the exact amount of gravel, river rock, and crushed stone you need for your landscaping project. Our free calculator provides accurate estimates in tons, cubic yards, and bags, helping you avoid ordering too much or too little material. Whether you’re building a driveway, walkway, garden bed, or drainage system, this tool accounts for compaction, waste factors, and material density to give you professional-grade calculations.

You’re standing in your backyard, measuring a new driveway space. You’ve got the length and width. You know roughly how deep you want the gravel. But here’s the problem: you have no idea how much rock to actually order.
Too little and you’re back at the supplier within days. Too much and you’ve wasted hundreds of dollars on material you don’t need.
This is where a rock calculator changes everything. Instead of guessing, you get exact numbers in seconds. You know the tons you need. You know the cubic yards. You even know how many bags to buy if you prefer smaller quantities.
Our rock calculator does all the heavy math for you. No formulas to memorize. No conversion charts. Just straightforward answers based on your specific project.

The Basic Formula

Here’s what you need to calculate rock quantities:

Volume (cubic yards) = Length × Width × Depth (in feet) ÷ 27

Weight (tons) = Cubic yards × Material density

Most gravel weighs 1.4 to 1.7 tons per cubic yard. We’ll break down each step below so you get accurate numbers for your specific project.

Most people call suppliers and ask, “How much gravel do I need?” The answer they get back? “About 5 tons, maybe 6.”

That vagueness costs money.

Here’s why a rock calculator is better:

It accounts for material density. Pea gravel weighs differently than river rock. Crushed granite isn’t the same weight as lava rock. A calculator knows all these densities. It doesn’t guess.

It handles compaction automatically. When you compact gravel for a driveway, the material settles and takes up less space. You need 30% more material than the raw calculation shows. Most people forget this. A good calculator includes it.

It adds the waste factor. Even professionals order 10% extra. Spillage happens. Ground is never perfectly level. Corners are hard to fill exactly. A calculator builds this in.

It gives you options. Want your estimate in tons? Cubic yards? Bags? A professional calculator switches between all three instantly.

It saves money on delivery. You order exactly what you need. No second trip. No “close enough” ordering that leaves you short.

How Our Rock Calculator Works (Step-by-Step)

The calculator is designed to be fast and simple. You don’t need to understand the math behind it. Just follow these steps:

Step 1: Choose Your Project Type

Select what you’re building:

• General landscaping
• Driveway
• Walkway or path
• Drainage area
• Garden bed or mulch
• Erosion control
• Patio base
• Playground surface

Why this matters: Different projects need different depths. A garden bed doesn’t need 4 inches of gravel like a driveway does. Choosing your project type automatically sets a recommended depth. You can change it if needed.

Step 2: Pick Your Area Shape

Most projects fit one of three shapes:

Rectangle – Driveways, patios, large garden beds. You measure length and width.

Circle – Tree rings, circular garden features. You measure the diameter.

Custom – Weird-shaped spaces. You calculate the total square footage yourself and enter it directly.

The calculator handles all three differently but gets you the right answer for each.

Step 3: Enter Your Measurements

Choose your units first. Are you comfortable with feet and inches? Or do you prefer meters and centimeters? The calculator works in both. Pick what’s easiest for you.

Then measure carefully:

• Length (for rectangles)
• Width (for rectangles)
• Diameter (for circles)
• Total area (for custom shapes)
• Depth of material you want

Take your time measuring. A 1-foot error in a 20-foot space seems small, but it affects your material quantity significantly.

Step 4: Select Your Rock Material

The calculator includes 15+ rock types:

Pea Gravel – Smooth stones, 3/8 inch. Great for walkways and gardens. Weighs 1.5 tons per cubic yard.

River Rock – Natural smooth stones, 1-5 inches. Beautiful but doesn’t compact. Weighs 1.55-1.6 tons per cubic yard.

Crushed Stone #57 – Angular 3/4-inch stones. Perfect for driveways because it compacts solid. Weighs 1.6 tons per cubic yard.

Crushed Stone #8 – Smaller stones, 3/8-1/2 inch. Better for finishing layers and smooth surfaces. Weighs 1.55 tons per cubic yard.

Crushed Granite – Durable angular stone. Excellent for high-traffic areas. Weighs 1.65 tons per cubic yard.

Decomposed Granite – Breaks down and compacts firm. Perfect for paths that need a solid feel. Weighs 1.7 tons per cubic yard.

Limestone – Affordable and versatile. Good for driveways and bases. Weighs 1.6 tons per cubic yard.

Lava Rock – Very light. Great for garden mulch and decorative work. Weighs only 0.8 tons per cubic yard.

And 7 more options – Including trap rock, marble chips, white rock, Mexican beach pebbles, slate chips, and riprap.

Each material has a different weight density. The calculator knows them all. It uses the right density for your chosen material.

Step 5: Account for Compaction and Waste

Two checkboxes help fine-tune your estimate:

Include 10% waste factor – This is almost always recommended. It covers spillage, uneven ground, and the small bit extra you always need. Turn this on unless you’re an experienced contractor.

Account for compaction (+30%) – Only available for materials that compact (crushed stone, granite, decomposed granite). If you’re building a driveway, turn this on. If you’re doing a garden bed with river rock, leave it off.

Step 6: Get Your Results

The calculator shows:

• Total tons needed – The most important number. This is what you order from the supplier.
• Cubic yards – Helpful if your supplier measures in yards instead of tons.
• Total weight in pounds – Useful if you’re renting equipment or calculating truck capacity.
• Bag equivalents – How many 50-lb or 40-lb bags equal your total. Great if you prefer buying bags for small projects.
• Estimated cost – If you enter a price per ton, the calculator multiplies it by your total. This gives you a budget number instantly.

Rock Density: Why It Matters

Not all rocks weigh the same. A cubic yard of lightweight lava rock weighs 0.8 tons. The same volume of dense trap rock weighs 1.85 tons. Using the wrong density throws off your entire calculation.

Common Rock Densities (Tons per Cubic Yard)

Material Type	Weight Range	Best For
Pea Gravel (3/8″)	1.4 – 1.5 tons	Walkways, patios, gardens
River Rock (1-3″)	1.55 – 1.6 tons	Drainage, decorative beds
Crushed Stone #57 (3/4″)	1.5 – 1.7 tons	Driveways, bases
Crushed Granite	1.6 – 1.65 tons	Driveways, high traffic
Decomposed Granite	1.65 – 1.7 tons	Paths, patios (compacts firm)
Limestone (crushed)	1.5 – 1.6 tons	Driveways, affordable option
Lava Rock	0.7 – 0.9 tons	Garden mulch, lightweight
Riprap (6″+)	1.7 – 2.0 tons	Erosion control, large rocks
Marble Chips	1.5 – 1.6 tons	Decorative landscaping

Pro tip: Always ask your supplier for the specific density of their material. Regional variations in stone composition can affect weight by 10-15%.

Calculating River Rock for Circular Areas

Garden features, tree rings, and decorative circles need different math.

Circle Formula

Volume = π × (radius²) × depth ÷ 27

Example: Tree Ring

You want river rock around a tree. The circle is 8 feet across (diameter), 3 inches deep.

Step 1: Find the radius (half the diameter) 8 feet ÷ 2 = 4 feet radius

Step 2: Convert depth to feet 3 inches ÷ 12 = 0.25 feet

Step 3: Calculate volume 3.14 × (4 × 4) × 0.25 ÷ 27 = 0.46 cubic yards

Step 4: Calculate weight 0.46 × 1.6 (river rock density) = 0.74 tons

You’d order 1 ton to ensure complete coverage with some extra.

The Compaction Factor: Why You Need 30% More

When you compact gravel for driveways or paths, the rocks settle and the volume reduces. Ignoring this means your driveway will be too thin.

Materials That Compact

• Crushed stone (angular edges lock together)
• Crushed granite
• Decomposed granite
• Limestone screenings
• Any “minus” material (like 3/4″ minus)

Materials That Don’t Compact Much

• Rounded river rock (rolls instead of locking)
• Large riprap
• Pea gravel (small, pre-settled)

If your project requires compaction, add 30% to your material order.

Example: You calculated 5 tons needed. 5 tons × 1.3 = 6.5 tons (order amount)

According to EPA guidelines on gravel roads, proper compaction can reduce volume by 25-30% depending on material type and compaction equipment used.

The Waste Factor: Always Add 10%

Real-world conditions mean you’ll need extra material:

• Irregular ground contours
• Slight measurement errors
• Spillage during transport
• Hard-to-reach corners
• Settling over time

Standard practice: Add 10% to every calculation.

Example: You need 5 tons after compaction adjustment. 5 tons × 1.1 = 5.5 tons final order

This small buffer saves you from running short and paying for a second delivery, which often costs $75-150.

How Much Does Gravel Cost? Real Pricing Guide

Material costs vary by region and type, but here are national averages:

Bulk Material Prices (per ton)

Material	Price Range	When to Use
Basic crushed stone	$30 – $45	Driveways, bases, functional areas
Pea gravel	$40 – $55	Walkways, decorative beds
River rock (1-3″)	$50 – $80	Landscaping, drainage
Decomposed granite	$40 – $60	Firm paths, modern landscapes
Lava rock	$60 – $100	Garden mulch, volcanic look
Mexican beach pebbles	$200 – $400	High-end decorative features
Marble chips	$45 – $70	Bright white accents

Additional Costs

Delivery: $50 – $150 depending on distance (free within 10 miles from many suppliers)

Landscape fabric: $0.10 – $0.30 per square foot

Edging: $1 – $8 per linear foot (plastic to metal)

Labor (if hiring): $30 – $60 per hour, or $0.50 – $1.50 per square foot installed

Common Mistakes People Make (And How the Calculator Prevents Them)

Mistake 1: Using Generic Gravel Density

Most people think all gravel weighs the same. It doesn’t.

Lava rock weighs 0.8 tons per cubic yard. Trap rock weighs 1.85 tons. That’s more than double.

If you use the wrong density, your entire order is wrong.

Our calculator prevents this by letting you choose your specific material. Each material has its accurate density built in.

Mistake 2: Forgetting About Compaction

Crushed stone locks together when compacted. A 5-ton base becomes a 6.5-ton order when you account for settling.

Most people forget this. They order 5 tons, compact it, and end up 1.5 tons short.

The calculator’s compaction checkbox handles this automatically.

Mistake 3: Not Adding Extra for Waste

Even professionals order 10% extra. Spillage, uneven ground, and measurement errors add up.

People who skip this often run short and have to pay premium delivery fees for a small second order.

The calculator’s waste factor option protects you from this mistake.

Mistake 4: Measuring Carelessly

One 10-foot driveway that’s actually 20 feet means you order half what you need.

Measure twice. Mark your area with spray paint. The calculator is only as good as your measurements.

Mistake 5: Choosing the Wrong Material Depth

A garden bed looks bad at 4 inches deep. A driveway looks bad at 2 inches.

The calculator recommends depths based on project type. These are industry standards, not guesses. Use them unless you have a specific reason to go deeper or shallower.

Real Examples: Using the Calculator for Different Projects

Example 1: Gravel Driveway

Project size: 20 feet long, 12 feet wide, 4 inches deep

Steps:

1. Select “Driveway” – Recommended depth: 4 inches ✓
2. Choose “Rectangle”
3. Enter: 20 feet length, 12 feet width
4. Depth is already 4 inches ✓
5. Select “Crushed Stone #57” (best for driveways)
6. Turn ON “Include 10% waste” ✓
7. Turn ON “Account for compaction” ✓

Results:

• Base calculation: 2.93 cubic yards
• With compaction: 3.81 cubic yards
• With waste: 4.19 cubic yards
• Total weight: 6.7 tons
• Order: 7 tons
• Cost at $45/ton: $315 material

Why this makes sense: Crushed stone compacts solid, so you need the compaction factor. Gravel spreads during delivery and installation, so the waste factor protects you.

Example 2: Pea Gravel Walkway

Project size: 30 feet long, 3 feet wide, 3 inches deep

Steps:

1. Select “Walkway/Path” – Recommended depth: 3 inches ✓
2. Choose “Rectangle”
3. Enter: 30 feet length, 3 feet width
4. Depth is already 3 inches ✓
5. Select “Pea Gravel”
6. Turn ON “Include 10% waste” ✓
7. Turn OFF “Account for compaction” (pea gravel is already settled)

Results:

• Base calculation: 0.83 cubic yards
• With waste: 0.91 cubic yards
• Total weight: 1.37 tons
• Bag equivalents: 55 bags (50-lb each)
• Order: 1.5 tons (or buy 75 bags if easier to transport)
• Cost at $55/ton: $82.50 material

Why this works: Pea gravel doesn’t need compaction – it’s naturally settled smooth. The waste factor still applies because you’ll overspill some during installation.

Example 3: Tree Ring with River Rock (Small)

Project size: 6-foot diameter circle, 3 inches deep

Steps:

1. Select “General Landscaping”
2. Choose “Circle”
3. Enter: 6 feet diameter
4. Depth: Change to 3 inches
5. Select “River Rock (1-2″)”
6. Turn ON “Include 10% waste” ✓
7. Turn OFF “Account for compaction” (river rock is decorative)

Results:

• Base calculation: 0.33 cubic yards
• With waste: 0.36 cubic yards
• Total weight: 0.58 tons
• Bag equivalents: 23 bags (50-lb each)
• Order: 1 ton (or buy 25 bags)
• Cost at $70/ton: $70 material

Why this works: River rock looks nice but you don’t compact it. The small waste factor still applies for spillage and edge coverage.

Example 4: River Rock Drainage Area

Project size: 15-foot long trench, 2-foot wide, 4 inches deep (French drain)

Steps:

1. Select “Drainage Area” – Recommended depth: 3-4 inches, use 4 inches
2. Choose “Rectangle”
3. Enter: 15 feet length, 2 feet width
4. Depth: Keep at 4 inches (or 3 inches minimum) ✓
5. Select “River Rock (3-5″)” (larger size for drainage)
6. Turn ON “Include 10% waste” ✓
7. Turn OFF “Account for compaction” (river rock doesn’t compact for drainage)

Results:

• Base calculation: 0.89 cubic yards
• With waste: 0.98 cubic yards
• Total weight: 1.57 tons
• Bag equivalents: 63 bags (50-lb each)
• Order: 1.75 tons (or buy 70 bags)
• Cost at $75/ton: $132 material

Why this works: Larger river rock (3-5 inches) is perfect for French drains. It allows water to flow freely between rocks while preventing soil from clogging the drain. The larger stones don’t compact like crushed stone would. You use more material per area, but drainage function is superior. The 10% waste factor covers spillage during installation and settling over time.

Pro tip for drainage: Some contractors use 2 feet wide, 4 inches deep trenches along foundation lines for water management. The calculator shows you need about 1.75 tons of large river rock for a 15-foot stretch. Double it for 30 feet (3.5 tons), and you can see how a basic drainage project budget builds up.

When to Use the Calculator vs. When to Get Professional Help

Use the Calculator When:

• You’re planning a DIY project
• You want to understand material quantities before calling suppliers
• You have a simple rectangular driveway or pathway
• You’re budgeting for a landscape design
• You want to compare different material options quickly
• You’re a contractor quoting multiple projects

Talk to a Professional When:

• Your space is very irregular or sloped
• You’re building something structural (retaining walls, bases for heavy equipment)
• Your project involves drainage that could affect building foundations
• You’re uncertain about soil conditions underneath
• Local regulations require engineering for your project

For most homeowner projects, the calculator is all you need. It’s accurate enough to order with confidence.

Pro Tips for Getting Perfect Results

Tip 1: Measure Multiple Times

Measure your space at least twice. Better yet, have someone double-check your measurements. A single error can throw off your entire order.

Tip 2: Account for Slopes

If your ground isn’t perfectly level, measure at the highest and lowest points. Use the higher number to be safe.

Tip 3: Plan for Future Settling

Gravel settles over 6-12 months. Some contractors recommend ordering 15% extra if you want to top-up later. The calculator’s 10% covers normal settling.

Tip 4: Call Your Supplier First

Ask what materials they have and their prices. Plug those into the calculator to get accurate cost estimates.

Tip 5: Order Extra Edge Space

Measure your exact project, then add 6 inches on all sides. Gravel spreads beyond your intended boundaries. The extra space prevents this.

Tip 6: Consider Two-Layer Installation

For driveways, use #57 stone for the base (3 inches) and #8 stone for the top layer (2 inches). Calculate each layer separately for accuracy.

Tip 7: Use the Calculator for Comparison

Calculate the same project with different materials. See how cost and weight change. This helps you choose the best material for your budget.

Calculator Results Explained

Cubic Yards Explained

A cubic yard is 3 feet × 3 feet × 3 feet. It’s a standard measurement in landscaping.

Why does it matter? Some suppliers measure gravel in cubic yards instead of tons. Knowing your cubic yard number helps you communicate with them clearly.

Tons Explained

Weight is how most large deliveries are priced. One ton of gravel costs $40-70 depending on material and location.

The calculator shows you how many tons you need. This is what you order from the supplier.

Bags vs. Bulk

Buying bags makes sense for small projects (under 1 ton) where you transport materials yourself.

Buying bulk makes sense for larger projects. It’s cheaper per unit and fewer pieces to handle.

The calculator shows both options. Choose what works for your situation.

How Material Density Affects Your Order

Different rocks weigh different amounts per cubic yard:

Material	Weight Per Cubic Yard	What This Means
Lava rock	0.8 tons	Lightest option. Great for gardens if you’re moving materials by hand.
Pea gravel	1.5 tons	Light and smooth. Easy to spread but doesn’t compact firm.
River rock	1.6 tons	Natural appearance but heavy. Doesn’t compact, so use for decoration not bases.
Crushed stone #57	1.6 tons	Standard driveway material. Compacts solid when driven on.
Decomposed granite	1.7 tons	Naturally compacts firm. Great for paths that need to feel solid.
Trap rock	1.85 tons	Heaviest common option. Maximum density and durability.

A cubic yard of lava rock weighs less than half what trap rock weighs. That’s why density matters.

If you order the wrong material, you get the wrong weight. If you get the wrong weight, your project fails (too thin, too soft, spreads too much).

The calculator prevents this by using the correct density for each material type.

Avoiding Second Delivery Fees

Here’s what actually happens when you guess:

1. You estimate 5 tons
2. You order 5 tons
3. Installation shows you’re short (happens more than you think)
4. You call back and order 1 more ton
5. Second delivery fee: $75-150
6. New material cost: $40-70

That “small” order cost you $115-220 when you include delivery.

With the calculator’s waste factor built in, you order 5.5 tons the first time. Cost: $15-20 extra material. You avoid the second delivery fee entirely.

Over your lifetime of projects, this alone pays for using a professional calculator.

Special Considerations for Different Climates

Cold Climates (Freeze/Thaw Areas)

Use 6-inch minimum depth for driveways. Freeze/thaw cycles cause heaving. Deeper gravel provides insulation and drainage.

USDA Extension offices recommend crushed angular stone over rounded river rock in areas with heavy frost.

Hot, Dry Climates

Decomposed granite performs excellently. It compacts firm and reflects less heat than darker stones. Water lightly and compact again after installation for maximum hardness.

High-Rainfall Areas

Increase depth by 1 inch for better drainage. Consider French drains alongside gravel surfaces to handle runoff. Use larger stone (3/4″ minimum) for better water flow.

Coastal Areas

Salt air accelerates limestone deterioration. Use granite, trap rock, or river rock instead. These materials resist salt damage.

Frequently Asked Questions:

Can I use this calculator for sand or soil?

The calculator is optimized for rock and gravel. Sand and soil have different densities and compaction properties. For sand or soil, contact your supplier for material-specific density information. They can adjust the calculator results accordingly.

What if my project has an unusual shape?

If your space is irregular, break it into smaller rectangles. Calculate each rectangle separately, then add the totals together. The calculator’s “Custom” area option is also available if you can measure your total square footage directly.

How accurate is this calculator compared to supplier estimates?

Professional supplier estimates are usually within 10% of calculator results. The calculator is actually more accurate than phone estimates because it accounts for compaction, waste, and specific material density. Call your supplier with your calculator results – they’ll confirm the numbers are solid.

Do I really need to account for compaction?

If you’re building a driveway, patio, or anything vehicles drive on – yes, absolutely. Compaction reduces volume by 25-30%. Skip it and your surface will be too thin. For decorative rocks in garden beds, compaction doesn’t apply.

What if I buy bags instead of bulk?

The calculator shows bag equivalents for 50-lb and 40-lb bags. Bags cost 3-4x more per ton than bulk, but make sense if you’re transporting materials yourself and your project is small. Use the bag numbers to calculate how many you need for the full project.