🌱 Mulch, Gravel & Topsoil Calculator
Enter your area and desired depth to get cubic yards, cubic feet, and estimated bags needed for mulch, gravel, or topsoil — no more guessing at the yard.
Last Updated: July 10, 2026
Enter Area & Depth
Material Needed
📊 Common Depths for Mulch, Gravel & Topsoil
| Application | Depth | Cubic Yards per 100 sq ft |
|---|---|---|
| Mulch top-up (existing bed) | 2 in | 0.617 |
| New mulch bed | 3 in | 0.926 |
| Gravel path / patio base | 4 in | 1.235 |
| Gravel driveway | 6 in | 1.852 |
💡 The Cubic Yard Formula, Explained
Cubic Yards = (Area in sq ft × Depth in inches) ÷ 324. This works because 1 cubic yard = 27 cubic feet, and there are 12 inches in a foot, so 27 × 12 = 324 — dividing directly by 324 converts square-foot-inches straight to cubic yards without extra steps.
🌱 How to Calculate Mulch, Gravel & Topsoil Needed
Step 1: Find the Area
Area (sq ft) = Length (ft) × Width (ft)
Example: 20 ft × 25 ft bed = 500 sq ft
Step 2: Find Cubic Feet
Cubic Feet = (Area × Depth in inches) ÷ 12
Example: 500 sq ft at 3 in deep = (500 × 3) ÷ 12 = 125 cubic feet
Step 3: Convert to Cubic Yards
Cubic Yards = Cubic Feet ÷ 27, which simplifies to (Area × Depth) ÷ 324
Example: 125 ÷ 27 = 4.63 cubic yards (matches 500 × 3 ÷ 324 = 4.63)
Step 4: Estimate Bags Needed
Bags = Cubic Feet ÷ 2 (rounded up), assuming standard 2-cubic-foot bags
Example: 125 ÷ 2 = 62.5, rounded up to 63 bags
💡 Real-World Examples & Use Cases
See how the area × depth ÷ 324 formula applies to real yard projects.
New 500 sq ft mulch bed at 3 inches deep
A homeowner is creating a new flower bed measuring 20 ft × 25 ft (500 sq ft), and wants a fresh 3-inch layer of mulch.
Result: 500 × 3 ÷ 324 = 4.63 cubic yards (125 cubic feet, or 63 bags at 2 cu ft each).
Topping up an existing 300 sq ft bed at 2 inches
An existing bed just needs a light refresh layer rather than a full new application.
Result: 300 × 2 ÷ 324 = 1.85 cubic yards (50 cubic feet, or 25 bags).
Gravel driveway, 800 sq ft at 6 inches deep
A gravel driveway needs a compacted 6-inch base layer over an 800 sq ft area.
Result: 800 × 6 ÷ 324 = 14.81 cubic yards (400 cubic feet) — bulk delivery is far more practical than bags at this volume.
⚠️ Common Mistakes & Pro Tips
- Forgetting to convert inches to feet: Depth must be handled in inches through the ÷324 (or ÷12 then ÷27) formula — mixing units gives wildly wrong totals.
- Not accounting for compaction: Gravel and topsoil settle after installation; add 5-10% extra material for compacted applications like driveways.
- Buying bags for large areas: Bags become expensive and impractical above roughly 2-3 cubic yards — bulk delivery is usually cheaper for anything larger.
- Using one depth for everything: Mulch top-ups, new beds, and gravel driveways all need different depths — check the reference table before ordering.
🔍 People Also Ask
How many bags of mulch do I need for 1 cubic yard?
About 13.5 standard 2-cubic-foot bags equal one cubic yard (27 ÷ 2 = 13.5), so most people round up to 14 bags.
How deep should a gravel driveway base be?
Most gravel driveways use a compacted base of 4 to 6 inches, sometimes more in areas with poor soil drainage.
Does mulch or gravel weigh more per cubic yard?
Gravel is significantly heavier, often 2,400-2,800 lbs per cubic yard, compared to mulch at roughly 400-800 lbs per cubic yard.
❓ Frequently Asked Questions
How much gravel do I need for a driveway?
Driveways typically need 4-6 inches of compacted gravel depth; use the same area × depth ÷ 324 formula to estimate cubic yards.
How many bags of mulch equal one cubic yard?
Standard 2-cubic-foot bags require 13.5 bags to equal one cubic yard (27 ÷ 2 = 13.5), so most people round up to 14 bags.
Should I buy mulch/gravel in bulk or bags?
Bulk (by the cubic yard) is more economical for areas larger than about 100 square feet; bags are more convenient for small touch-up jobs.
How much topsoil do I need to fill a raised garden bed?
Use the same volume formula: length × width × desired depth, converted to cubic yards or cubic feet, since topsoil is sold by volume just like mulch and gravel.
Does the calculator account for settling or compaction?
No, the calculator provides raw volume needed; add 5-10% extra for materials that settle over time, such as loose topsoil or mulch.
How much does a cubic yard of mulch weigh?
Roughly 400-800 lbs depending on moisture content and material type, which matters for delivery truck capacity and spreading effort.
Can I mix depth zones, like thicker mulch near trees?
Yes, calculate each zone separately with its own area and depth, then add the cubic yard results together for your total material order.