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Lava Rock Calculator

Calculate lava rock for decorative landscape beds, fire pit fill, drainage, and ground cover. Lightweight volcanic stone (red or black) — exact cubic yards, bags, and cost.

You'll need
1.48 cu yd · 20 bags
Cost
$150–$375
Project details
Areas
Area 1
LengthWidthside viewDepth
Area: 160 sq ftVolume: 40 cu ft
Total160 sq ft · 40.00 cu ft
Material
Lava Rock · Lightweight volcanic rock. Decorative — black or red.
Default depth: 3"Density: ~35 lbs/cu ft
How you'll buy it
💡 Bulk delivery recommended
Your project is ≥1 cubic yard — bulk is usually half the cost of 20 bags.

Leave blank to use estimate

Default: $100–$250/yd

Typical: $50–$120

Extras

Plastic, metal, or stone edging

Cost breakdown

Showing bulk delivery pricing (recommended for your volume).
Lava Rock · 1.50 cu yd$150 – $375
Total project cost$150 – $375
💡 Comparison: 20 bags would cost $140 – $240; bulk (1.50 yd) would cost $150 – $375.

Shopping list

Everything you need for this project.
  • Lava Rock (bulk delivery)1.50 cu yd
  • Wheelbarrow1
  • Garden rake & flat shovel1 set
  • Gloves1 pair
  • Tamper or hand compactor (for compaction)optional
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Get quotes from local landscape supply yards.
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Math breakdown

Step-by-step from your inputs.
Area 1 · 20 × 8 × 3"/1240 cu ft
Total volume40.00 cu ft
Cubic yards · ÷ 271.48 cu yd
Bags · ÷ 2 cu ft per bag20 bags
Weight · @ 35 lbs/cu ft1,400 lbs (0.70 tons)

Pro tips

Lighter than other rock. Lava rock weighs ~35 lbs per cubic foot, vs. ~100 for gravel. Easier to haul and spread by hand. Downside: blows or washes away in storms more easily.

Red or black — pick based on plants. Red lava rock pops against green plants but clashes with red brick. Black lava rock is more neutral, works with any color scheme. Black holds heat — bad for plants in hot climates.

Doesn't decompose. Unlike wood mulch, lava rock never breaks down — install once, never replace. Top dress with fresh rocks every 5-10 years for fresh color (UV fades it over time).

Frequently asked questions

How much lava rock for a 100 sq ft bed?▾
At 3 inches deep: about 1 cubic yard. Lava rock weighs much less than other stone (about 0.5 tons per yard vs. 1.4 for gravel), so it ships and handles easier.
Lava rock for fire pits — safe?▾
Yes for outdoor fire pits and gas-fueled fire features. Don't use in enclosed wood stoves or fireplaces. Lava rock can crack and pop with rapid heating; use specifically-rated fire rock for high-temperature use.
Does lava rock attract bugs?▾
No more than any other stone. The porous surface holds water briefly after rain but doesn't provide food for bugs the way wood mulch does.
Will lava rock kill grass underneath?▾
Yes — a 2-3 inch layer smothers grass over a few weeks. For best results, kill or remove grass first, lay landscape fabric, then add lava rock on top.

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Disclaimer. This calculator provides estimates for planning purposes. Actual material quantities and costs may vary based on site conditions, material availability, and local pricing.