Lava Rock Calculator
Calculate cubic yards of lava rock for low-maintenance landscaping and fire pits
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Tips & Notes
- •2"–3" depth is standard for decorative landscape beds.
- •Lava rock is extremely lightweight — roughly 1/2 the weight of regular gravel.
- •It won't decompose or float like organic mulch, making it a low-maintenance choice.
- •Red lava rock (cinders) is cheaper than black; both work well for fire pit surrounds.
- •Install landscape fabric underneath to prevent weeds from growing through.
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Materials & Supplies
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Pro tips for lava rock
- ›2"–3" depth is standard for decorative landscape beds.
- ›Lava rock is extremely lightweight — roughly 1/2 the weight of regular gravel.
- ›It won't decompose or float like organic mulch, making it a low-maintenance choice.
- ›Red lava rock (cinders) is cheaper than black; both work well for fire pit surrounds.
- ›Install landscape fabric underneath to prevent weeds from growing through.
Frequently asked questions
How much lava rock do I need for a 100 sq ft bed?▾
At 2"–3" depth, 100 sq ft needs 0.6–0.9 cubic yards (roughly 6–9 bags at 2 cu ft each, or 1 cubic yard delivered). Lava rock is much lighter than other landscape rock so bagged is practical for small projects.
Is lava rock good for fire pits?▾
Yes — lava rock is heat-resistant and works well as a filler in propane fire pits and around wood-burning pits. It absorbs and radiates heat. Don't use river rock or limestone in fires — they can trap moisture and crack or explode.
Red vs. black lava rock — what's the difference?▾
Red lava rock (cinders, scoria) is the most common and cheapest at $30–$60/yard. Black lava rock is denser and harder to source, running $80–$150/yard. Both work identically for landscaping and fire applications.
How long does lava rock last?▾
Indefinitely — lava rock doesn't decompose like wood mulch and doesn't wash away easily. It can fade slightly in direct sun over 5+ years but otherwise lasts the life of the landscape bed.
Does lava rock kill plants?▾
No, but it absorbs heat which can stress nearby plants in hot climates. It also doesn't add organic matter, so plants in lava rock beds need separate fertilization. It's not suitable as a soil amendment.