Fire Glass Calculator
Find how much fire glass your fire pit or fireplace needs. Pick a round or rectangular burner pan, enter its size and the fill depth, choose a glass type, and get the pounds of fire glass, the volume, the number of bags, and the cost — with by-depth and by-glass-type tables and a downloadable PDF.
| Depth | Volume | Weight | Bags |
|---|---|---|---|
| Enter a pan to see depths | |||
| Glass | Density | Weight | Cost |
|---|---|---|---|
| Enter a pan to compare | |||
How to use the fire glass calculator
Pick a round or rectangular burner, enter its size and the fill depth, choose a glass type, and get the pounds of fire glass, the volume, the number of bags and the cost — with by-depth and by-glass-type tables and a downloadable PDF.
Choose the shape
Rectangle uses length × width; round uses the diameter. Measure the inside of the pan, not the outer rim.
Enter size & depth
Add the dimensions in inches or feet, then the fill depth — 2–3″ covers most burners.
Pick the glass type
¼″, ½″, large/lump glass or lava rock — this sets the density used to turn volume into weight.
Add bags & price, save a PDF
Get the bag count and cost, compare depths and glass types, and download it for the store.
How the fire glass estimate is calculated
Fire glass is sold by weight, but a pan is measured by size and depth. The estimate bridges the two in three steps — area, then volume, then weight by the density of the glass you choose.
Worked example — 24″ × 12″ pan, 2″ deep, ¼″ glass
Area: 24 × 12 = 288 sq in
Volume: 288 × 2 ÷ 1,728 = 0.33 cu ft
Weight: 0.33 × 105 = 35 lb
Bags: 35 ÷ 10 = 3.5 → 4 bags
Cost (at $4/lb): 35 × 4 = $140
A 24 × 12-inch pan filled 2 inches deep needs about 35 lb of ¼″ fire glass — four 10-lb bags, giving a little spare to top off and level.
Fire glass reference charts
The numbers that come up most — how the weight reacts to fill depth, how much common pan sizes need, and the density of each glass type.
| Fill depth | Volume | Weight | 10-lb bags |
|---|---|---|---|
| 1 in | 0.17 cu ft | 17.5 lb | 2 |
| 1.5 in | 0.25 cu ft | 26.3 lb | 3 |
| 2 in | 0.33 cu ft | 35.0 lb | 4 |
| 3 in | 0.50 cu ft | 52.5 lb | 6 |
| 4 in | 0.67 cu ft | 70.0 lb | 7 |
Weight scales straight with depth — doubling the fill doubles the pounds. Most burners are covered well at 2–3 inches, so going deeper mostly adds cost.
| Pan size | Area | Volume | Weight | 10-lb bags |
|---|---|---|---|---|
| 18 in round | 254 sq in | 0.29 cu ft | 31 lb | 4 |
| 24 in round | 452 sq in | 0.52 cu ft | 55 lb | 6 |
| 24 × 12 in rect | 288 sq in | 0.33 cu ft | 35 lb | 4 |
| 30 × 12 in rect | 360 sq in | 0.42 cu ft | 44 lb | 5 |
| 48 × 12 in rect | 576 sq in | 0.67 cu ft | 70 lb | 7 |
Values rounded. A 3-inch fill is roughly 1.5× these weights; lighter media such as lava rock needs fewer pounds for the same pan.
| Glass type | Density | Notes |
|---|---|---|
| ¼″ fire glass | ~105 lb/ft³ | Most common; packs tight, heaviest per cubic foot |
| ½″ fire glass | ~100 lb/ft³ | Larger pieces, slightly lighter fill |
| Large / lump glass | ~90 lb/ft³ | Chunky, decorative, lighter still |
| Lava rock | ~55 lb/ft³ | Lightest and lowest cost; good base layer |
Reflective and standard fire glass weigh about the same — the number is the fill density, which is what turns volume into pounds. Switching type changes the weight, not the volume.
The amount of fire glass comes from three things: the pan’s area and the fill depth set the volume, and the glass density turns that volume into a weight — the pounds and bags you actually buy.
- Area and depth set the volume — a bigger pan or a deeper fill means more glass, in direct proportion.
- Density sets the weight — the same volume weighs more in ¼″ glass than in lava rock.
- Bags round up — buy whole bags, and the spare helps you top off and level the surface.
Everything the calculator works out
One set of inputs gives you the weight, the volume, the burner area, the number of bags and the cost — plus a comparison across depths and glass types, and a report for the store.
The figures behind every fill
Built for anyone filling a fire pit or fireplace
A backyard fire pit, a linear fire table, an indoor gas fireplace — the area-depth-density math is the same, and knowing the pounds and bags before you shop means one trip and no half-empty pan.
Filling a round or square fire pit and wanting the right amount to cover the burner cleanly without overbuying.
- Measure the inside of the pan
- Start with a 2″ fill
- Buy a little extra to level
Building or filling a long linear burner where the length drives the quantity and the look matters.
- Use the rectangle mode
- Compare glass types for cost
- Keep glass off the ports
Spec’ing media for gas fireplaces and pits across jobs, with a clean estimate and a cost figure per unit.
- Match depth to the maker’s spec
- Price per pound for quotes
- Save the PDF to the job file
7 tips for buying fire glass right
The small things that leave a pan short or a burner choked — and the checks that get you the right fill the first time.
Fire glass FAQ
The quantity, depth and cost questions people ask most when filling a fire pit or fireplace with fire glass.
Multiply the burner area by the fill depth to get the volume, then multiply by the glass density to get the weight. A 24-inch by 12-inch pan filled 2 inches deep with ¼″ glass holds about 0.33 cu ft, which is roughly 35 pounds.
At 10 pounds per bag that’s four bags, since fire glass is bought in whole bags. The calculator does this for any round or rectangular pan and rounds the bag count up so you order enough to fill it.
A fill depth of 2 to 3 inches is typical — enough to cover the burner by about 1 to 2 inches so it’s hidden but still gets airflow. Less than that may leave the pan showing; much more just adds cost without improving the look.
Always keep the glass clear of the burner ports so it doesn’t choke the flame, and follow the appliance maker’s depth and clearance guidance. The calculator’s by-depth table shows how the weight changes as you go deeper.
Fire glass is most commonly sold in 10-pound and 25-pound bags, with 5-pound jars and larger boxes also available. The calculator lets you pick the bag size and rounds your total up to whole bags.
Because it rounds up, you’ll usually have a little spare — which is handy for topping off and leveling the surface after the first burn settles the glass.
The volume stays the same, but the weight changes with density. Smaller glass packs tighter — about 105 pounds per cubic foot for ¼″ — while ½″ glass, large or lump glass, and lava rock are progressively lighter, down to around 55 pounds per cubic foot for lava rock.
So switching media changes the pounds and the number of bags, not the space you’re filling. The by-glass-type table compares them side by side for your pan.
For a round pan, area is π ÷ 4 × diameter². Multiply that by the fill depth and divide by 1,728 to get cubic feet, then multiply by the glass density for the weight.
In the calculator, choose the Round shape and enter the diameter instead of length and width — everything else works the same. A 24-inch round pan at 2 inches deep with ¼″ glass needs about 55 pounds, or six 10-pound bags.
Yes. Lava rock fills the same volume as fire glass but weighs much less — about 55 pounds per cubic foot versus 105 for ¼″ glass — so you need fewer pounds for the same pan.
Select Lava rock as the glass type and the weight, bag count and cost update automatically. It’s a lighter, lower-cost base, and some people use it under a thinner top layer of fire glass.
Fire glass commonly runs about $3 to $6 per pound depending on type and color, with reflective glass usually costing more than standard. Lava rock is cheaper per pound.
Enter a price per pound in the calculator and it estimates the total cost for the weight you need. Pricing varies by supplier and quantity, so treat the figure as a planning estimate and confirm with your supplier.
It’s a close estimate. The area and volume math is exact, but real-world weight varies with glass size, shape and how it settles, so your actual pounds can differ slightly from the calculated figure.
Buy a little extra to top off and level the surface, and always follow the appliance maker’s instructions for approved media, fill depth and clearances. For installation and safety specifics, defer to the manufacturer.
Estimate Only — Follow the Appliance Maker: This calculator uses volume × density to estimate fire glass weight — volume = area × fill depth ÷ 1,728, and weight = volume × glass density — with typical fire-glass densities that vary with glass size, shape and type. Fill depth is usually 2–3 inches, enough to cover the burner by about 1–2 inches, and the glass must be kept clear of the burner ports. Actual weight can differ with how the glass settles, so buy a little extra to top off and level. Use only media, depths and clearances approved for your specific burner or fireplace. For reference and estimating only; always follow the appliance manufacturer’s instructions for approved media, fill depth and safe operation.