Fire Pit Details
Materials Needed
How Much Fire Glass Do I Need?
The answer depends on your fire pit's shape and size, how deep you want to fill it, and the type of glass or media you're using. Different materials have different densities — reflective glass weighs about 90 lbs per cubic foot while lava rock is only 55 lbs per cubic foot, so the same volume looks very different on a scale at the store.
Pounds = (Area in sq inches × Depth in inches ÷ 1,728) × Density (lb/ft³)
Divide by 1,728 to convert cubic inches to cubic feet. Densities: reflective glass 90, tempered 85, lava rock 55.
For a 36-inch round fire pit with 3 inches of tempered fire glass: area = π × 18² = 1,017 sq in. Volume = 1,017 × 3 ÷ 1,728 = 1.77 cu ft. Weight = 1.77 × 85 = ~150 lbs. That's approximately 15 bags. Our calculator handles all three shapes and six material types automatically.
Fire Glass Pounds by Fire Pit Size — Quick Reference
The table below assumes 3-inch fill depth with tempered fire glass (85 lb/ft³). Adjust proportionally for other depths or materials.
| Fire Pit Size | Shape | Approx. Pounds (3" depth) | 10-lb Bags |
|---|---|---|---|
| 24" diameter | Round | ~65–75 lbs | 7–8 bags |
| 36" diameter | Round | ~145–160 lbs | 15–16 bags |
| 48" diameter | Round | ~255–280 lbs | 26–28 bags |
| 30" × 30" | Square | ~125–140 lbs | 13–14 bags |
| 48" × 24" | Rectangle | ~145–160 lbs | 15–16 bags |
| 60" × 8" | Linear burner | ~60–70 lbs | 6–7 bags |
Fire Glass Types Compared
| Material | Density (lb/ft³) | Price/lb | Appearance | Best For |
|---|---|---|---|---|
| Reflective Fire Glass | 90 | $3.00–$4.50 | Mirror-like sparkle | Maximum visual impact |
| Tempered Fire Glass | 85 | $2.00–$3.00 | Clear to colored glow | Best value, most popular |
| Crushed Fire Glass | 80 | $1.50–$2.50 | Textured, varied sizes | Budget-friendly coverage |
| Lava Rock | 55 | $1.00–$2.00 | Natural, rustic | Base layer, low cost |
| Ceramic Balls | 60 | $2.50–$3.50 | Modern, round | Contemporary look |
| River Rock (fire-rated) | 95 | $1.50–$2.50 | Natural stone | Rustic/natural aesthetic |
Fill Depth: How Much Is Right?
The depth of your fill affects appearance, cost, and burner performance. The sweet spot for most residential fire pits is 2 to 3 inches. At 2 inches the glass fully covers the burner and looks clean; at 3 inches you get a more lush, premium appearance. Beyond 4 inches you're spending more money without meaningful visual improvement, and you risk restricting gas flow.
- 1–2 inches: Accent layer over lava rock base — cost-effective strategy
- 2–3 inches: Standard full fill — covers burner, looks full and complete
- 3–4 inches: Premium look — deeper color, more sparkle visible at night
- 4+ inches: Diminishing returns — can reduce flame height and gas efficiency
Never use regular glass, marbles, or decorative stones in a fire pit. Regular glass will shatter when heated. River rocks can contain trapped moisture that turns to steam and causes explosive cracking. Only use glass specifically rated for fire pits (1,200°F minimum) or ceramic/lava media designed for gas burners.
The Money-Saving Layering Technique
The most effective way to reduce fire glass cost is the layering strategy: fill the bottom 1–2 inches with lava rock (about $1/lb) and add 1–2 inches of fire glass on top. The lava rock is completely hidden and costs roughly one-third of reflective fire glass. For a 36-inch round pit this approach can save $100–$200 compared to filling entirely with premium glass, with no visible difference in the final look.
Option 1: All reflective glass (3" depth)
~160 lbs × $4/lb = $640
Option 2: 1.5" lava rock + 1.5" reflective glass
~80 lbs lava rock × $1.50/lb = $120
~80 lbs reflective glass × $4/lb = $320
Total = $440 — saves $200
Worked Calculation Examples
Example 1: 36-inch round fire pit, 3" tempered glass
- Radius = 18 inches
- Area = π × 18² = 1,017 sq in
- Volume = 1,017 × 3 ÷ 1,728 = 1.77 cu ft
- Weight = 1.77 × 85 lb/ft³ = 150 lbs / 15 bags
Example 2: 48" × 24" rectangular fire table, 2" crushed glass
- Area = 48 × 24 = 1,152 sq in
- Volume = 1,152 × 2 ÷ 1,728 = 1.33 cu ft
- Weight = 1.33 × 80 lb/ft³ = 107 lbs / 11 bags
Buying Tips
Fire glass is sold in 10-lb and 50-lb bags. The 50-lb option costs less per pound but commits you to one color and requires hauling a heavier bag. For most projects under 200 lbs, 10-lb bags give you flexibility to mix colors and stop when you have enough.
When comparing prices, check the price per pound rather than per bag. Online retailers often have better selection than home centers. American Fireglass and similar specialty suppliers sell at closer to wholesale pricing for larger quantities. Look for free shipping thresholds — fire glass is heavy and shipping can add $20–$50 to a small order.
Installation Checklist
- Verify your burner is rated for fire glass media (most modern gas burners are)
- Clean the fire pit interior, remove any debris
- Add lava rock base layer if using the layering approach
- Pour fire glass evenly — use a kitchen strainer to remove dust first
- Spread level with a trowel or gloved hands
- Ensure burner ports are not buried — glass should sit ½" below burner top
- Test ignition and check flame height before finalizing fill depth
- Add or remove glass to adjust flame appearance as desired
Density values are approximate averages and vary by manufacturer and specific product. Always verify with your supplier for exact specifications. Prices shown are general market ranges and fluctuate. Gas fire pit installation involving new gas lines should be performed by a licensed professional.
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